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Ching-Wu Chu

Publications and source records attributed to Ching-Wu Chu.

At least 19 recordsLinked to original sources

Can LLMs extract scientific consensus? A case study in high-temperature superconductivity

Scientific knowledge is increasingly dispersed across vast and heterogeneous scientific literature, where important claims are often implicit, evolving, and internally debated. While large language models (LLMs) have shown impressive performance in information extraction and summarization, their ability to recover latent scientific consensus remains unclear. Here, we investigate this problem in the context of high-temperature superconductivity (HTS), a long-standing and highly debated topic in condensed matter physics, as a challenging testbed. Using near 18,000 highly-cited publications over the past seven decades, we construct a structured knowledge graph linking competing superconducting mechanisms, material families, evidential modalities, and citation relations. We find that LLM-extracted representations recover coherent and physically interpretable structures, including family-dependent mechanism profiles, evidence-specific correlations, and citation-mediated temporal evolution of scientific beliefs. Ablation studies on LLM further show that the global structure remains robust across prompting, decoding, and model variations. Our results suggest that LLMs can indeed serve as scalable tools for deciphering scientific knowledge in domains characterized by competing interpretations and evolving knowledge.

cs.DL

Pressure-induced Superconductivity in AgSbTe2

AgSbTe2 is a well-known thermoelectric material with a high Seebeck coefficient and intrinsically low thermal conductivity, but its behavior under pressure remains largely unexplored. Here we report a systematic investigation of the structural, electronic, and transport properties of non-stoichiometric AgSbTe2 under high pressure. At ambient pressure, the material can be described as having a cubic crystal structure that remains stable up to 21.7 GPa beyond which it loses long-range structural order, while its crystal system fully recovers upon decompression. Remarkably, superconductivity emerges at a very low pressure of 0.38 GPa with an onset superconducting critical temperature (Tc) of 3.2 K. Tc increases with increasing pressure, reaching 6.9 K at 31.9 GPa, and peaks at 7.4 K during decompression. Magnetic-field-dependent transport measurements and electronic structure calculations reveal an evolution of the superconducting state driven by an enhanced electronic density of states at the Fermi level under compression. Our findings uncover pressure-induced superconductivity in AgSbTe2 and demonstrate that pressure can effectively tune the electronic ground state of thermoelectric materials, extending their functionality beyond thermoelectric energy conversion.

cond-mat.supr-con

Ambient-pressure 151-K superconductivity in HgBa2Ca2Cu3O8+{\delta} via pressure quench

Superconductivity has been a vigorously researched topic since its discovery in 1911. Raising the superconducting transition temperature (Tc) has been the main driving force behind such long-sustained efforts due to its potential for impacting humanity and the fundamental knowledge gained from understanding this macroscopic coherent quantum state at high temperatures. The successful development of high-Tc superconductivity will make possible extraordinarily efficient generation, delivery, and utilization of energy, and could also enable the development of controlled fusion while impacting other burgeoning fields like quantum computation and quantum electronics. However, progress has been hindered by a longstanding plateau in the record ambient-pressure Tc, unchanged since 1993. Subsequent significant advancements in Tc have been achieved only under high pressures, preventing the realization of superconductivity's full potential. To directly address this challenge, we developed a pressure-quench protocol (PQP) to stabilize pressure-induced/-enhanced superconducting states at ambient pressure. Here we achieve a record ambient-pressure Tc of 151 K in the cuprate HgBa2Ca2Cu3O8+{\delta} via PQP. The experimental results are further supported by synchrotron X-ray diffraction measurements and phonon and electronic structure calculations. This breakthrough opens new avenues for stabilizing and exploring ambient-pressure high-Tc superconducting states and other quantum states that have been previously only accessible under pressure, paving the way for deeper understanding and practical applications of high-Tc superconductivity and beyond.

cond-mat.supr-con

High-pressure stabilization of Mg2IrH7: Structural proximity to high-Tc superconductivity

Mg$_2$IrH$_6$ is a metastable complex metal hydride with a predicted superconducting transition temperature as high as 170 K at ambient pressure. Following the synthesis of isomorphic, insulating Mg$_2$IrH$_5$ at low pressure, higher-pressure studies were conducted to investigate the phase behavior and compound formation in this system. X-ray diffraction and Raman spectroscopic measurements indicate that cubic Mg$_2$IrH$_7$ is stabilized above ca. 40 GPa and coexists with a related hexagonal hydride with likely composition near Mg$_2$IrH$_5$. Electrical transport measurements show that the cubic Mg$_2$IrH$_7$ is insulating, in agreement with ab initio predictions, and persists during room-temperature decompression until $\sim$20 GPa before reverting back to the cubic Mg$_2$IrH$_5$. The experimental results confirm ground-state structure predictions in the Mg-Ir-H system, and the formation of two nearly identical phases with surrounding compositions opens new opportunities to access superconducting Mg$_2$IrH$_6$ through non-equilibrium processing pathways.

cond-mat.supr-con

Diamond-to-graphite transformation under hypersonic impact

Diamond to graphite transformation is a complex kinetically driven process which has been studied under various conditions for its fundamental importance. We report the transformation of diamond embedded ceramic matrix composites during hypersonic impact. Diamond particles embedded in cubic boron nitride matrix provide a superhard composite that was subjected to high impact collisions of metal projectiles travelling at speeds reaching Mach 8.45. Our observations suggest that the energy absorption and fracture of the composite is primarily enabled via the phase change of diamond into graphite. Characterization of the impact-fractured composite shows transformed diamond particles and provides details of the shock-induced phase transformation and the nature of diamond-graphite interfaces formed during rapid phase change. The study provides new understanding of phase transformation of diamond under extreme conditions.

cond-mat.mtrl-sci

Evidence for itinerant electron-local moment interaction in Li-doped $\alpha$-MnTe

We use inelastic neutron scattering (INS) and angle-resolved photoemission spectroscopy (ARPES) to study the impact of Li doping on the semiconducting altermagnet $\alpha$-MnTe. Introducing Li results in a spin reorientation from in-plane to out-of-plane direction and increases the density of itinerant carriers. While our ARPES measurements do not indicate any notable doping-induced changes in the electronic band structure or the magnitude of the altermagnetic band splitting, our INS measurements reveal an abrupt carrier-induced decrease in the spin wave lifetime near the zone boundary at high energies. This finding is consistent with a new magnon decay channel driven by doping-induced subtle changes in the band structure and enhanced interactions between Mn$^{2+}$ local moments and itinerant electrons. By extracting the local dynamic susceptibility from INS spectra and applying the total moment sum rule, we find that both undoped and Li-doped $\alpha$-MnTe exhibit the full expected Mn$^{2+}$ local moment of $\approx5.9~\mu_\mathrm{B}$ with $S=5/2$. These findings suggest that $\alpha$-MnTe hosts robust local-moment altermagnetism which shows a breakdown at high energies upon addition of itinerant carriers, highlighting the importance of carrier-spin coupling in magneto-transport and spin dynamic properties of altermagnets even in the dilute-carrier limit.

cond-mat.str-el

Strain-tunable anomalous Hall effect in hexagonal MnTe

The ability to control and manipulate time-reversal ($T$) symmetry-breaking phases with near-zero net magnetization is a sought-after goal in spintronic devices. The recently discovered hexagonal altermagnet manganese telluride ($\alpha$-MnTe) is a prime example. It has a compensated altermagnetic ground state where the magnetic moments are aligned in each layer and stacked antiparallel along the $c$ axis, yet it exhibits a spontaneous anomalous Hall effect (AHE) that breaks the $T$-symmetry with a vanishingly small $c$-axis ferromagnetic (FM) moment. However, the presence of three 120$^\circ$ separated in-plane magnetic domains presents a challenge in understanding the origin of the AHE and the effective control of the altermagnetic state. Here we use neutron scattering to show that symmetry breaking anisotropic strain, induced by compressive uniaxial pressure along the nearest-neighbor (NN) Mn-Mn bond directions, detwins $\alpha$-MnTe into a single in-plane magnetic domain. This control over in-plane domains allows us to unambiguously establish that the in-plane moments are aligned along the NNN Mn-Mn bond direction, irrespective of the applied strain directions. Mounting the sample on a piezoelectric strain cell along both NN and NNN directions can drive the sample into a single-domain state that significantly sharpens the AHE hysteresis loop and extends the AHE to lower temperatures. Furthermore, tuning the uniaxial strain reverses the sign of the AHE near room temperature. Remarkably, this is achieved without altering the altermagnetic phase-transition temperature or substantially changing the small $c$-axis FM moment. Combined with our phenomenological model, we argue that these effects result from the modification of the electronic Berry curvature by a combination of both spin-orbit coupling and strain. (See the full abstract in the PDF.)

cond-mat.str-el

Creation, stabilization, and study at ambient pressure of pressure-induced superconductivity in Bi$_{0.5}$Sb$_{1.5}$Te$_3$

In light of breakthroughs in superconductivity under high pressure, and considering that record critical temperatures (T$_c$s) across various systems have been achieved under high pressure, the primary challenge for higher Tc should no longer solely be to increase T$_c$ under extreme conditions but also to reduce, or ideally eliminate, the need for applied pressure in retaining pressure-induced or -enhanced superconductivity. The topological semiconductor Bi$_{0.5}$Sb$_{1.5}$Te$_3$ (BST) was chosen to demonstrate our approach to addressing this challenge and exploring its intriguing physics. Under pressures up to ~ 50 GPa, three superconducting phases (BST-I, -II, and -III) were observed. A superconducting phase in BST-I appears at ~ 4 GPa, without a structural transition, suggesting the possible topological nature of this phase. Using the pressure-quench protocol (PQP) recently developed by us, we successfully retained this pressure-induced phase at ambient pressure and revealed the bulk nature of the state. Significantly, this demonstrates recovery of a pressure-quenched sample from a diamond anvil cell at room temperature with the pressure-induced phase retained at ambient pressure. Other superconducting phases were retained in BST-II and -III at ambient pressure and subjected to thermal and temporal stability testing. Superconductivity was also found in BST with T$_c$ up to 10.2 K, the record for this compound series. While PQP maintains superconducting phases in BST at ambient pressure, both depressurization and PQP enhance its T$_c$, possibly due to microstructures formed during these processes, offering an added avenue to raise T$_c$. These findings are supported by our density-functional theory calculations.

cond-mat.supr-con

Field-Resilient Supercurrent Diode in a Multiferroic Josephson Junction

The research on supercurrent diodes has surged rapidly due to their potential applications in electronic circuits at cryogenic temperatures. To unlock this functionality, it is essential to find supercurrent diodes that can work consistently at zero magnetic field and under ubiquitous stray fields generated in electronic circuits. However, a supercurrent diode with robust field tolerance is currently lacking. Here, we demonstrate a field-resilient supercurrent diode by incorporating a multiferroic material into a Josephson junction. We first observed a pronounced supercurrent diode effect at zero magnetic field. More importantly, the supercurrent rectification persists over a wide and bipolar magnetic field range beyond industrial standards for field tolerance. By theoretically modeling a multiferroic Josephson junction, we unveil that the interplay between spin-orbit coupling and multiferroicity underlies the unusual field resilience of the observed diode effect. This work introduces multiferroic Josephson junctions as a new field-resilient superconducting device for cryogenic electronics.

cond-mat.supr-con

Pressure-induced superconductivity in a novel germanium allotrope

High-pressure studies on elements play an essential role in superconductivity research, with implications for both fundamental science and applications. Here we report the experimental discovery of surprisingly low pressure driving a novel germanium allotrope into a superconducting state in comparison to that for alpha-Ge. Raman measurements revealed structural phase transitions and possible electronic topological transitions under pressure up to 58 GPa. Based on pressure-dependent resistivity measurements, superconductivity was induced above 2 GPa and the maximum Tc of 6.8 K was observed under 4.6 GPa. Interestingly, a superconductivity enhancement was discovered during decompression, indicating the possibility of maintaining pressure-induced superconductivity at ambient pressure with better superconducting performance. Density functional theory analysis further suggested that the electronic structure of Ge (oP32) is sensitive to its detailed geometry and revealed that disorder in the beta-tin structure leads to a higher Tc in comparison to the perfect beta-tin Ge.

cond-mat.supr-con

Room-temperature ferromagnetism in epitaxial bilayer FeSb/SrTiO3(001) terminated with a Kagome lattice

Two-dimensional (2D) magnets exhibit unique physical properties for potential applications in spintronics. To date, most 2D ferromagnets are obtained by mechanical exfoliation of bulk materials with van der Waals interlayer interactions, and the synthesis of single or few-layer 2D ferromagnets with strong interlayer coupling remains experimentally challenging. Here, we report the epitaxial growth of 2D non-van der Waals ferromagnetic bilayer FeSb on SrTiO3(001) substrates stabilized by strong coupling to the substrate, which exhibits in-plane magnetic anisotropy and a Curie temperature above 300 K. In-situ low-temperature scanning tunneling microscopy/spectroscopy and density-functional theory calculations further reveal that a Fe Kagome layer terminates the bilayer FeSb. Our results open a new avenue for further exploring emergent quantum phenomena from the interplay of ferromagnetism and topology for application in spintronics.

cond-mat.mtrl-sci

Quantum paramagnetism in a non-Kramers rare-earth oxide: Monoclinic $\rm Pr_2Ti_2O_7$

Little is so far known about the magnetism of the $\rm A_2B_2O_7$ monoclinic layered perovskites that replace the spin-ice supporting pyrochlore structure for $r_A/r_B>1.78$. We show that high quality monoclinic Pr$_2$Ti$_2$O$_7$ single crystals with a three-dimensional network of non-Kramers Pr$^{3+}$ ions that interact through edge-sharing super-exchange interactions, form a singlet ground state quantum paramagnet that does not undergo any magnetic phase transitions down to at least 1.8 K. The chemical phase stability, structure, and magnetic properties of the layered perovskite Pr$_2$Ti$_2$O$_7$ were investigated using x-ray diffraction, transmission electron microscopy, and magnetization measurements. Synthesis of polycrystalline samples with the nominal compositions of Pr$_2$Ti$_{2+x}$O$_7$ ($-0.16 \leq x \leq 0.16$) showed that deviations from the Pr$_2$Ti$_2$O$_7$ stoichiometry lead to secondary phases of related, structures including the perovskite phase Pr$_{2/3}$TiO$_3$ and the orthorhombic phases Pr$_4$Ti$_9$O$_{24}$ and Pr$_2$TiO$_5$. No indications of site disordering (stuffing and anti-stuffing) or vacancy defects were observed in the Pr$_2$Ti$_2$O$_7$ majority phase. A procedure for growth of high-structural-quality, stoichiometric single crystals of Pr$_2$Ti$_2$O$_7$ by the traveling solvent floating zone (TSFZ) method is reported. Thermo-magnetic measurements of single-crystalline Pr$_2$Ti$_2$O$_7$ reveal an isolated singlet ground state that we associate with the low symmetry crystal electric field environments that split the $2J+1=9$-fold degenerate spin-orbital multiplets of the four differently coordinated Pr$^{3+}$ ions into 36 isolated singlets resulting in an anisotropic temperature independent van-Vleck susceptibility at low $T$. A small isotropic Curie term is associated with 0.96(2)\% non-interacting Pr$^{4+}$ impurities.

cond-mat.mtrl-sci

Observation of Flat Bands and Dirac Cones in a Pyrochlore Lattice Superconductor

Emergent phases often appear when the electronic kinetic energy is comparable to the Coulomb interactions. One approach to seek material systems as hosts of such emergent phases is to realize localization of electronic wavefunctions due to the geometric frustration inherent in the crystal structure, resulting in flat electronic bands. Recently, such efforts have found a wide range of exotic phases in the two-dimensional kagome lattice, including magnetic order, time-reversal symmetry breaking charge order, nematicity, and superconductivity. However, the interlayer coupling of the kagome layers disrupts the destructive interference needed to completely quench the kinetic energy. Here we demonstrate that an interwoven kagome network-a pyrochlore lattice-can host a three dimensional (3D) localization of electron wavefunctions. Meanwhile, the nonsymmorphic symmetry of the pyrochlore lattice guarantees all band crossings at the Brillouin zone X point to be 3D gapless Dirac points, which was predicted theoretically but never yet observed experimentally. Through a combination of angle-resolved photoemission spectroscopy, fundamental lattice model and density functional theory calculations, we investigate the novel electronic structure of a Laves phase superconductor with a pyrochlore sublattice, CeRu$_2$. We observe flat bands originating from both the Ce 4$f$ orbitals as well as from the 3D destructive interference of the Ru 4$d$ orbitals. We further observe the nonsymmorphic symmetry-protected 3D gapless Dirac cones at the X point. Our work establishes the pyrochlore structure as a promising lattice platform to realize and tune novel emergent phases intertwining topology and many-body interactions.

cond-mat.str-el

Structure and equation of state of $Bi_2Sr_2Ca_{n-1}Cu_nO_{2n+4+δ}$ from x-ray diffraction to megabar pressures

Pressure is a unique tuning parameter for probing the properties of materials and has been particularly useful for studies of electronic materials such as high-temperature cuprate superconductors. Here we report the effects of quasi-hydrostatic compression produced by a neon pressure-medium on the structures of bismuth-based high $\mathit{T_c}$ cuprate superconductors with the nominal composition $Bi_2Sr_2Ca_{n-1}Cu_nO_{2n+4+δ}$ (n=1,2,3) up to 155 GPa. The structures of all three compositions obtained by synchrotron X-ray diffraction can be described as pseudo-tetragonal over the entire pressure range studied. We show that previously reported pressure-induced distortions and structural changes arise from the large strains that can be induced in these layered materials by non-hydrostatic stresses. The pressure-volume equations of state (EOS) measured under these quasi-hydrostatic conditions cannot be fit to single phenomenological formulation over the pressure ranges studied, starting below 20 GPa. This intrinsic anomalous compression as well as the sensitivity of $Bi_2Sr_2Ca_{n-1}Cu_nO_{2n+4+δ}$ to deviatoric stresses provides explanations for the numerous inconsistencies in reported EOS parameters for these materials. We conclude that the anomalous compressional behavior of all three compositions is a manifestation of the changes in electronic properties that are also responsible for the remarkable non-monotonic dependence of $\mathit{T_c}$ with pressure, including the increase in $\mathit{T_c}$ at the highest pressures studied so far for each. Transport and spectroscopic measurements up to megabar pressures are needed to fully characterize and explore still higher possible critical temperatures in these materials.

cond-mat.supr-con

Pressure-induced high-temperature superconductivity retained at ambient

To raise the superconducting-transition temperature (Tc) has been the driving force for the long, sustained effort in superconductivity research. Recent progress in hydrides with Tcs up to 287 K under 267 GPa has heralded a new era of room-temperature superconductivity (RTS) with immense technological promise. Indeed, RTS has lifted the temperature barrier for the ubiquitous application of superconductivity. Unfortunately, formidable pressure is required to attain such high Tcs. The most effective relief to this impasse is to remove the pressure needed while retaining the pressure-induced Tc without pressure. Here we show such a possibility in the pure and doped high-temperature superconductor (HTS) FeSe by retaining, at ambient via pressure-quenching (PQ), its Tc up to 37 K (quadrupling that of a pristine FeSe) and other pressure-induced phases. We have also observed that some phases remain stable without pressure at up to 300 K and for at least 7 days. The observations are in qualitative agreement with our ab initio simulations using the solid-state nudged elastic band (SSNEB) method. We strongly believe that the PQ technique developed here can be adapted to the RTS hydrides and other materials of value with minimal effort.

cond-mat.supr-con

Fermion-boson many-body interplay in a frustrated kagome paramagnet

Kagome-net, appearing in areas of fundamental physics, materials, photonic and cold-atom systems, hosts frustrated fermionic and bosonic excitations. However, it is extremely rare to find a system to study both fermionic and bosonic modes to gain insights into their many-body interplay. Here we use state-of-the-art scanning tunneling microscopy and spectroscopy to discover unusual electronic coupling to flat-band phonons in a layered kagome paramagnet. Our results reveal the kagome structure with unprecedented atomic resolution and observe the striking bosonic mode interacting with dispersive kagome electrons near the Fermi surface. At this mode energy, the fermionic quasi-particle dispersion exhibits a pronounced renormalization, signaling a giant coupling to bosons. Through a combination of self-energy analysis, first-principles calculation, and a lattice vibration model, we present evidence that this mode arises from the geometrically frustrated phonon flat-band, which is the lattice analog of kagome electron flat-band. Our findings provide the first example of kagome bosonic mode (flat-band phonon) in electronic excitations and its strong interaction with fermionic degrees of freedom in kagome-net materials.

cond-mat.mtrl-sci

Room-temperature skyrmion phase in bulk Cu2OSeO3 under high pressures

A skyrmion state in a non-centrosymmetric helimagnet displays topologically protected spin textures with profound technological implications for high density information storage, ultrafast spintronics, and effective microwave devices. Usually, its equilibrium state in a bulk helimagnet occurs only over a very restricted magnetic-field--temperature phase space and often in the low temperature region near the magnetic transition temperature Tc. We have expanded and enhanced the skyrmion phase region from the small range of 55-58.5 K to 5-300 K in single-crystalline Cu2OSeO3 by pressures up to 42.1 GPa through a series of phase transitions from the cubic P2(_1)3, through orthorhombic P2(_1)2(_1)2(_1) and monoclinic P2(_1), and finally to the triclinic P1 phase, using our newly developed ultrasensitive high-pressure magnetization technique. The results are in agreement with our Ginzburg-Landau free energy analyses, showing that pressures tend to stabilize the skyrmion states and at higher temperatures. The observations also indicate that the skyrmion state can be achieved at higher temperatures in various crystal symmetries, suggesting the insensitivity of skyrmions to the underlying crystal lattices and thus the possible more ubiquitous presence of skyrmions in helimagnets.

cond-mat.str-el

Revealing the Origin of Luminescence Center in 0D Cs4PbBr6 Perovskite

Zero dimensional perovskite Cs4PbBr6 has attracted considerable attention recently not only because of its highly efficient green photoluminescence (PL), but also its two highly debated opposing mechanisms of the luminescence: embedded CsPbBr3 nanocrystals versus intrinsic Br vacancy states. After a brief discussion on the root cause of the controversy, we provide sensitive but non-invasive methods that can not only directly correlate luminescence with the underlying structure, but also distinguish point defects from embedded nanostructures. We first synthesized both emissive and non-emissive Cs4PbBr6 crystals, obtained the complete Raman spectrum of Cs4PbBr6 and assigned all Raman bands based on density functional theory simulations. We then used correlated Raman-PL as a passive structure-property method to identify the difference between emissive and non-emissive Cs4PbBr6 crystals and revealed the existence of CsPbBr3 nanocrystals in emissive Cs4PbBr6. We finally employed a diamond anvil cell to probe the response of luminescence centers to hydrostatic pressure. The observations of fast red-shifting, diminishing and eventual disappearance of both green emission and Raman below Cs4PbBr6 phase transition pressure of ~3 GPa is compatible with CsPbBr3 nanocrystal inclusions as green PL emitters and cannot be explained by Br vacancies. The resolution of this long-lasting controversy paves the way for further device applications of low dimensional perovskites, and our comprehensive optical technique integrating structure-property with dynamic pressure response is generic and can be applied to other emerging optical materials to understand the nature of their luminescent centers.

cond-mat.mtrl-sci