arXiv subjects

Hechang Lei

Publications and source records attributed to Hechang Lei.

At least 37 records · Page 2Linked to original sources

arXiv2025

Evidence for Anion-Free-Electron Duality and Enhanced Superconducting Role of Interstitial Anionic Electrons in Electrides

The discovery of superconducting electrides, characterized by interstitial anionic electrons (IAEs) residing in lattice cavities, has established a distinctive platform for investigating superconductors. Yet the superconducting origin and the fundamental role of IAEs in Cooper pairing formation remain poorly understood due to the challenges in directly observing IAEs. Here, combining angle-resolved photoemission spectroscopy (ARPES), transport measurements, and first-principles calculations, we certify that the IAEs in electride La3In (Tc = 9.4 K) exhibit a dual nature as both anions and free electrons. With the finite-depth potential well model, we trace that IAEs originate from electronic states near the Fermi level located above potential barriers, forming a Fermi sea susceptible to scattering by La-derived phonons, triggering superconductivity. ARPES combined with high-resolution XRD measurements on oxygen-treated samples directly reveals IAEs' spatial distribution and energy dispersion from interstitial sites with the consistent energy value predicted by our theory model. The concomitant diminution of free electrons upon oxygen treatment, leading to a marked reduction in superconductivity, further provides compelling experimental evidence that IAEs actively participate in electron-phonon coupling. Our findings resolve the long-standing ambiguity regarding the electronic nature of IAEs, elucidate their enhancing superconductivity in the phonon-mediated mechanism, and provide a foundation for exploring advanced electride-based superconductors.

cond-mat.supr-con↗

arXiv2025

Relationship among Structural, Disordered, Magnetism and Band Topology in MnSb2Te4(Sb2Te3)n Family

Interplay between topology and magnetism induces various exotic quantum phenomena, with magnetic topological insulators (MTIs) serving as a prominent example due to their ability to host the quantum anomalous Hall effect (QAHE). However, the realization of QAHE at higher temperature approaching magnetic-transition-temperature remains a significant challenge, primarily due to the scarcity of suitable material platforms and limited understanding of the intricate relationships between band topology, magnetism, and defects. Here, we report a comprehensive investigation of MnSb2Te4(Sb2Te3)n (n = 0 - 5) single crystals, including the discovery of novel MnSb8Te13 pure phase. Experimental measurements confirm that MnSb8Te13 exhibits ferromagnetism and features topologically nontrivial electronic structures, characterized by a Dirac point located further from the conduction band and a possible larger bulk gap compared to MnBi2Te4(Bi2Te3)n (n = 0 - 3). Moreover, we systematically analyze the relationship between structure, magnetism, topology, and disorder within Mn(Sb, Bi)2Te4((Sb, Bi)2Te3)n family. Present work will shed light on the exploration of potential platforms capable of achieving QAHE near magnetic transition temperature, offering new directions for advancing topological quantum materials.

cond-mat.mtrl-sci↗

arXiv2025

Superconductivity in kagome metal YRu3Si2 with strong electron correlations

We report the detailed physical properties of YRu3Si2 with the Ru kagome lattice at normal and superconducting states. The results of resistivity and magnetization show that YRu3Si2 is a type-II bulk superconductor with Tc ~ 3.0 K. The specific heat measurement further suggests that this superconductivity could originate from the weak or moderate electron-phonon coupling. On the other hand, both large Kadawaki-Woods ratio and Wilson ratio indicate that there is a strong electron correlation effect in this system, which may have a connection with the featured flat band of kagome lattice.

cond-mat.supr-con↗

arXiv2025

Pronounced orbital-selective electron-electron correlation and electron-phonon coupling in V2Se2O

Orbital-selective many-body effects, in which electrons occupying different orbitals experience distinct interaction strengths, play a crucial role in correlated multiorbital materials. However, these effects usually manifest in a complex manner, obscuring their microscopic origins. Here, by combining angle-resolved photoemission spectroscopy measurements with theoretical calculations, we reveal pronounced orbital selectivity in both electron-electron correlation and electron-phonon coupling in the van der Waals material V2Se2O. Electron correlation induces distinct bandwidth renormalization exclusively in the V d_xy-derived band, while the bands mainly composed of the other d orbitals remain essentially unrenormalized. Orbital-resolved analyses identify that the filling number and the bandwidth are decisive factors governing orbital-dependent correlation. Simultaneously, the d_(xz/yz)-derived band exhibits a sharp kink anomaly, arising from enhanced coupling to high-energy phonon modes dominated by oxygen vibrations. Such pronounced orbital selectivity positions V2Se2O as a rare and prototypical platform for unravelling the microscopic mechanisms of orbital-selective electron-electron and electron-phonon interactions, and offers guiding principles for the design of correlated multiorbital materials.

cond-mat.str-el↗

arXiv2025

Highly Efficient Room-Temperature Nonvolatile Magnetic Switching by Current in Fe3GaTe2 Thin Flakes

Effectively tuning magnetic state by using current is essential for novel spintronic devices. Magnetic van der Waals (vdW) materials have shown superior properties for the applications of magnetic information storage based on the efficient spin torque effect. However, for most of known vdW ferromagnets, the ferromagnetic transition temperatures lower than room temperature strongly impede their applications and the room-temperature vdW spintronic device with low energy consumption is still a long-sought goal. Here, we realize the highly efficient room-temperature nonvolatile magnetic switching by current in a single-material device based on vdW ferromagnet Fe3GaTe2. Moreover, the switching current density and power dissipation are about 300 and 60000 times smaller than conventional spin-orbit-torque devices of magnet/heavy-metal heterostructures. These findings make an important progress on the applications of magnetic vdW materials in the fields of spintronics and magnetic information storage.

cond-mat.mtrl-sci↗

arXiv2025

Superconductivity in cubic La3Al with interstitial anionic electrons

We report the observation of superconductivity in cubic La3Al single crystal. It shows a metallic behavior at a normal state without observable structural transition and enters the superconducting state below Tc ~ 6.32 K. Detailed characterizations and analysis indicate that cubic La3Al is a bulk type-II BCS superconductor. Moreover, theoretical calculations show that it can host interstitial anionic electrons, which are located at the body center of cubic unit cell, and confirm the electron-phonon coupling as the superconducting mechamism. Thus, cubic La3Al can be regarded as an novel electride superconductor.

cond-mat.supr-con↗

arXiv2025

Evolution of ultra-flat band in van der Waals kagome semiconductor Pd3P2(S1-xSex)8

We investigate the evolutions of structural parameters, optical properties, and electronic structures of van der Waals kagome semiconductor Pd3P2S8 with Se doping. When the doping level of Se increases, the bandgaps of Pd3P2(S1-xSex)8 single crystals decrease gradually, accompanying with the expanded unit cells. The first-principles calculations show that there is a flat band (FB) near the Fermi level in bulk Pd3P2S8. This FB mainly originates from the dz2-like orbitals of Pd atoms in the Pd kagome lattice, which has a finite interlayer electron hopping perpendicular to the PdS4 square plane. The interlayer hopping can be reinforced with the Se doping, inducing a stronger interlayer coupling via the chalcogen atoms at apical sites, which reduces the bandgap and enhances the cleavage energy. In contrast, the vanishing interlayer hopping in the two-dimensional limit results in the formation of ultra-FB in the monolayers of these compounds. The easy exfoliation and the existence of unique ultra-FB near EF make Pd3P2(S1-xSex)8 a model system to explore the exotic physics of FB in two-dimensional kagome lattice.

cond-mat.mtrl-sci↗

arXiv2025

Weakly superconducting anisotropy in 4Hb-Nb0.95Ti0.05Se2 with 1T/1H heterostructure

Heterostructures of layered transition metal dichalcogenide (TMD) exhibit rich physical properties by the combination of strong electronic correlation effects in 1T layer and superconductivity in 1H layer. But the limited number of bulk TMD materials with such heterostructures impedes the in-depth understanding of the physical mechanisms behind these properties, as well as research on tuning of these properties. Here, we report a systematic study on physical properties of the 4Hb-Nb0.95Ti0.05Se2 single crystals with 1T/1H heterostructure. It exhibits a superconducting transition at temperature below 3.3 K. Further analysis indicates that 4Hb-Nb0.95Ti0.05Se2 is an intermediately coupled type-II superconductor. Moreover, 4Hb-Nb0.95Ti0.05Se2 shows a rather weak superconducting anisotropy (~ 2), distinctly different from other known TMD superconductors with 4Hb heterostructure.

cond-mat.supr-con↗

arXiv2025

Charge-polarized superconducting state emerging in a superatomic antipolar metal

The simultaneous presence of polarity and metallicity or superconductivity in a material signifies the exotic polar metallic or superconducting (SC) state, while such materials are extremely rare due to their exclusive nature. Recently, the interweaved CDW and antipolar charge orders have been discovered in a metallic superatomic crystal of Au6Te12Se8 (ATS), while their interplay and competition with the following emergent SC state remains elusive. Here, we report a further experimental investigation of the SC state emerged from the preformed CDW and antipolar order states using scanning tunneling microscopy/spectroscopy in combination with transport and Raman measurements. The temperature-dependent pre-formation and condensation of Cooper pairs are experimentally identified. The pre-existent CDW is gradually suppressed by the preformed Cooper pairs, and then the antipolar charge order is spatially suppressed into a ferrielectric-like polar order by the condensed Cooper pairs of SC state. The exotic charge-polarized superconducting state is discovered in the polar metal of ATS, suggesting a valuable platform for the exploration of intriguing polar superconducting properties.

cond-mat.supr-con↗

arXiv2025

Magnetism of kagome metals $\left(\text{Fe}_{1-x} \text{Co}_{x}\right) \text{Sn}$ studied by $μ$SR

We study the magnetic properties of the metallic kagome system $\left(\mathrm{Fe}_{1-x} \mathrm{Co}_{x}\right) \mathrm{Sn}$ by a combination of Muon Spin Relaxation ($μ\mathrm{SR}$), magnetic susceptibility and Scanning Tunneling Microscopy (STM) measurements, in single crystal specimens with Co concentrations $\mathrm{x}=0,0.11,0.8$. In the undoped antiferromagnetic compound FeSn, we find possible signatures for a previously unidentified phase that sets in at $T^*\sim 50$ K, well beneath the Neel temperature $T_N \sim 376$ K, as indicated by a peak in the relaxation rate $1/T_1$ observed in zero field (ZF) and longitudinal field (LF) $μ\mathrm{SR}$ measurements, with a corresponding anomaly in the ac and dc-susceptibility, and an increase in the static width $1/T_2$ in ZF measurements. No signatures of spatial symmetry breaking are found in STM down to $7$ K. In $\mathrm{Fe}_{0.2} \mathrm{Co}_{0.8} \mathrm{Sn}$, we find canonical spin glass behavior with freezing temperature $T_{g} \sim 3.5 \mathrm{~K}$; the ZF and LF time spectra exhibit results similar to those observed in dilute alloy spin glasses CuMn and AuFe, with a critical behavior of $1 / T_{1}$ at $T_{g}$ and $1 / \mathrm{T}_{1}\rightarrow 0$ as $T \rightarrow 0$. The absence of spin dynamics at low temperatures makes a clear contrast to the spin dynamics observed by $μ\mathrm{SR}$ in many geometrically frustrated spin systems on insulating kagome, pyrochlore, and triangular lattices. The spin glass behavior of CoSn doped with dilute Fe moments is shown to originate primarily from the randomness of doped Fe moments rather than due to geometrical frustration of the underlying lattice.

cond-mat.str-el↗

arXiv2025

Nodeless superconductivity in 4H$_{b}$-TaS$_{2}$ with broken time reversal symmetry

The transition metal dichalcogenide 4H$_{b}$-TaS$_{2}$ exhibits characteristics of topological edge modes and two-component superconductivity with time-reversal symmetry breaking (TRSB). The nature of the superconducting order parameter is a crucial issue that requires experimental investigation. Here, we report measurements of the magnetic penetration depth using a tunnel-diode-oscillator based technique, as well as the specific heat. Both the specific heat and the change in magnetic penetration depth ($Δ$$λ$(T)) display an exponentially-activated temperature dependence, providing evidence for nodeless superconductivity in 4H$_{b}$-TaS$_{2}$. Moreover, the deduced superfluid density can be well described by a two-gap $s$-wave model, and such multigap superconductivity is consistent with there being multiple bands crossing the Fermi energy. These results constrain the possible pairing symmetries of 4H$_{b}$-TaS$_{2}$.

cond-mat.supr-con↗

arXiv2025

Intriguing kagome topological materials

Topological quantum materials with kagome lattice have become the emerging frontier in the context of condensedmatter physics. Kagome lattice harbors strongmagnetic frustration and topological electronic states generatedby the unique geometric configuration.Kagomelattice has the peculiar advantages in the aspectsofmagnetism, topology aswell as strong correlationwhenthe spin, charge,ororbit degreesof free is introduced, and providing a promising platform for investigating the entangled interactionsamongthem. In this paper, we will systematically introduce the research progress on the kagome topological materials and give a perspective in the framework of the potential future development directions in this field.

cond-mat.supr-con↗

arXiv2025

High Pressure Growth of Transition-Metal Monosilicide RhGe Single Crystals

Transition-metal monosilicide RhGe has been reported to exhibit weak itinerant ferromagnetism, superconductivity, and topological properties. In this study, we report the high-pressure growth of high-quality RhGe single crystals up to millimeter size using flux method. Transport measurements reveal the metallic behavior of RhGe between 2-300 K with Fermi liquid behavior at low temperature region. However, no superconductivity was observed with variations in Ge composition. Magnetic characterizations indicate that RhGe exhibits a paramagnetic behavior between 2-300 K. The high-quality, large-size RhGe single crystals pave the way for further investigation of their topological properties using spectroscopic techniques.

cond-mat.str-el↗

arXiv2025

Observation of topological Anderson Chern insulator phase in MnBi$_4$Te$_7$ monolayer

The correlation of topology and disorder has attracted great intention due to appropriate disorder could induce the phase transition between trivial and nontrivial topological states. While it is widely recognized that strong disorder can produce rich phase diagrams in topological nontrivial states, moderate disorder has been proposed to induce transitions into topologically nontrivial phases counter-intuitively, leading to the concept of topological Anderson insulators. This phenomenon has been theoretically explored and simulated in various systems, yet experimental realization in solid state systems has remained elusive due to challenges in controlling disorder. Here, we report the experimental observation of Chern insulator state signed by the coexistence of quantized Hall plateau and zero longitudinal resistance in monolayer MnBi$_4$Te$_7$ Hall bar device, which originally hosts a trivial insulating state with Chern number $C$ = 0 in clean limit. We demonstrate that the observed trivial to nontrivial transition in this monolayer device can be attributed to disorder, evidenced by universal conductance fluctuations. Our findings substantiate the existence of a long-sought topological Anderson Chern insulator in real materials, a unique variant of the topological Anderson insulator characterized by broken time-reversal-symmetry.

cond-mat.mes-hall↗

arXiv2025

High-pressure modulation of breathing kagome lattice: Cascade of Lifshitz transitions and evolution of the electronic structure

The interplay between electronic correlations, density wave orders, and magnetism gives rise to several fascinating phenomena. In recent years, kagome metals have emerged as an excellent platform for investigating these unique properties, which stem from their itinerant carriers arranged in a kagome lattice. Here, we show that electronic structure of the prototypical kagome metal, Fe$_3$Sn$_2$, can be tailored by manipulating the breathing distortion of its kagome lattice with external pressure. The breathing distortion is suppressed around 15 GPa and reversed at higher pressures. These changes lead to a series of Lifshitz transitions that we detect using broadband and transient optical spectroscopy. Remarkably, the strength of the electronic correlations and the tendency to carrier localization are enhanced as the kagome network becomes more regular, suggesting that breathing distortion can be a unique control parameter for the microscopic regime of the kagome metals and their electron dynamics.

cond-mat.str-el↗

arXiv2024

Evidence for multiband gapless superconductivity in the topological superconductor candidate 4Hb-TaS2

We present the ultralow-temperature thermal conductivity measurements on single crystals of transition-metal dichalcogenide material 4Hb-TaS$_{2}$, which has recently been proposed as a topological superconductor candidate. In zero field, a small residual linear term $κ_{0}/T$ is observed, indicating the existence of a residual density of states in the superconducting state. The slow field dependence of $κ_{0}/T$ at low fields rules out the presence of nodes in the superconducting gap, and the S-shaped field dependence across the full field range suggests multiple superconducting gaps in 4Hb-TaS$_{2}$. Our results provide evidence for multiband gapless superconductivity in 4Hb-TaS$_{2}$, and the residual density of states come from certain gapless Fermi surfaces.

cond-mat.supr-con↗

arXiv2024

Uniaxial strain tuning of charge modulation and singularity in a kagome superconductor

Tunable quantum materials hold great potential for applications. Of special interest are materials in which small lattice strain induces giant electronic responses. The kagome compounds AV3Sb5 (A = K, Rb, Cs) provide a testbed for such singular electronic states. In this study, through angle-resolved photoemission spectroscopy, we provide comprehensive spectroscopic measurements of the giant responses induced by compressive and tensile strains on the charge-density-wave (CDW) order parameter and high-order van Hove singularity (HO-VHS) in CsV3Sb5. We observe a tripling of the CDW gap magnitudes with ~1% strain, accompanied by the changes of both energy and mass of the saddle-point fermions. Our results reveal an anticorrelation between the unconventional CDW order parameter and the mass of a HO-VHS, and highlight the role of the latter in the superconducting pairing. The giant electronic responses uncover a rich strain tunability of the versatile kagome system in studying quantum interplays under lattice perturbations.

cond-mat.mtrl-sci↗

arXiv2024

Interstitial anionic electrons involved superconductivity and T-linear resistivity behavior in electride La3In

Electrides are unique materials because of the existence of interstitial anionic electrons (IAEs). Due to these loosely bound IAEs and their strong interaction with the framework of cations, electrides can host superconductivity with rather high Tc, especially under high pressure, as predicted in theory. However, the experimental observations of superconductivity in electrides are very rare, let alone the detailed studies on intrinsic properties of single crystals. Here, we report the superconducting and normal-state properties of electride La3In single crystals. La3In shows a type-II superconductivity with Tc ~ 9.4 K and a T-linear resistivity in a wide temperature range. Experimental measurements and theoretical calculations suggest that the relatively high Tc could be ascribed to the high density of states around the Fermi level caused by short flat bands along R-M direction and the strong electron-phonon coupling, partially derived from the IAEs. Meanwhile, the T-linear resistivity may reflect the significant electronic correlation effect in this material. These findings will shed light on understanding the role of IAEs in superconductivity and open a promising way to explore high-temperature superconductors in electrides.

cond-mat.supr-con↗