arXiv subjects

Joe D. Thompson

Publications and source records attributed to Joe D. Thompson.

At least 19 recordsLinked to original sources

arXiv2026

High-quality single crystals of the kagome metals Ni$_3$In and Ni$_3$Sn grown from Pb flux

The bilayer kagome metal Ni$_3$In has recently attracted attention due to the presence of a flat band located near the Fermi level, which has been associated with unconventional thermodynamic and electronic transport properties [Ye et al., Nat. Phys. 20, 610-614 (2024)]. However, further investigation of the intrinsic properties of this system has been hindered by the lack of large, high-quality single crystals. Here, we report the successful growth of Ni$_3$(In, Sn) single crystals using a Pb-flux technique. By optimizing the growth conditions, competing binary phases can be effectively suppressed, enabling the synthesis of single crystals with dimensions reaching several millimeters. We compare the physical properties of our Pb-flux-grown crystals to previously reported samples prepared by iodine-assisted chemical vapor transport and molecular beam epitaxy as well as to first-principles resistivity calculations. We find a significantly lower electrical resistivity in our crystals, in excellent agreement with calculations of resistivity from electron-phonon scattering, a sizeable non-saturating magnetoresistance, and a reduced Sommerfeld coefficient and magnetic susceptibility compared to previous experimental findings, which are likely related to differences in the Fermi level position. Our results establish Pb-flux growth as a reliable route for obtaining large single crystals of the bilayer kagome metals Ni$_3$(In, Sn) that are suitable for further thermodynamic and spectroscopic investigations of their intrinsic electronic and magnetic properties.

cond-mat.mtrl-sci↗

arXiv2026

The Kondo effect in ferromagnetic quantum critical CeRh$_6$Ge$_4$

The mechanism of a pressure-induced quantum critical point in the heavy fermion ferromagnet CeRh$_6$Ge$_4$ has attracted interest, as ferromagnetic quantum criticality in a clean itinerant Ce compound is typically avoided. The localized versus itinerant character of the 4\textit{f} electrons is a key aspect for understanding this behavior. We investigated the electronic structure of the 4\textit{f} shell in CeRh$_6$Ge$_4$ using core-level photoelectron and x-ray absorption spectroscopy, demonstrating the hybridization of Ce 4\textit{f} with the conduction electrons. Linearly polarized x-ray absorption reveals a temperature-dependent linear dichroism consistent with the crystal-electric-field (CEF) sequence as inferred from the static susceptibility. This dichroism cannot be described by an ionic full-multiplet model alone, but is reproduced by including the Kondo effect within a single-impurity Anderson model in the non crossing approximation (SIAM/NCA). The Kondo effect mixes higher lying crystal-field states into a resulting multiorbital ground state with 4\textit{f} occupancy \textit{n}$_f$\,$\sim$\,0.9. Deviations at low temperatures between the measured linear dichroism and calculated dichroism suggest an orbital-dependent Kondo effect. A scenario in which there is a multiorbital ground state and orbital-dependent Kondo hybridization should be a starting point for a model of pressure-induced criticality in CeRh$_6$Ge$_4$.

cond-mat.str-el↗

arXiv2025

Evidence for easy-plane XY ferromagnetism in heavy-fermion quantum-critical CeRh6Ge4

We report $^{73}$Ge nuclear quadrupole resonance (NQR) and magnetic resonance (NMR) spectroscopy in the heavy-fermion quantum-critical ferromagnet CeRh$_6$Ge$_4$. NQR and NMR spectral measurements at the two non-equivalent Ge sites reveal electric field gradient tensors and the directions of their principal axes relative to the hexagonal basal plane. The spin-lattice relaxation rate $1/T_1$ experiments reveal a clear critical slowing down approaching the ferromagnetic transition. $1/T_1$ in the paramagnetic state is found to be predominantly caused by fluctuating 4$f$-local moments. The Knight shift shows Curie-Weiss behavior at high temperature and a deviation from this below $T^\ast$ $\approx$ 25 K possibly due to a mixture of crystalline electric field effects and Kondo screening. Order-parameter-like behavior of hyperfine fields at the Ge sites and ferromagnetic signal enhancement are observed in Zeeman-perturbed NQR, with uniform ferromagnetic order and a small ordered moment of $\approx$ 0.26 $\mu_B$/Ce confined within the $ab$-plane. The ordered moment shows a notable in-plane magnetic stiffness against out-of-plane radiofrequency fields and has an (XY-type) in-plane isotropic nature. Our results reveal a strong easy-plane anisotropy of 4$f$-electron moment and suggest an involved interplay of hybridization and local moment physics in this quantum critical heavy-fermion ferromagnet.

cond-mat.str-el↗

arXiv2025

Hydrostatic pressure studies on non-superconducting UTe2

We report the temperature-pressure phase diagram of a UTe$_2$ single crystal that does not undergo a bulk superconducting transition but shows filamentary superconductivity with a critical transition temperature of 1 K at ambient pressure. Electrical-resistivity measurements reveal that the evolution of the filamentary superconducting state under pressure resembles the behavior observed in previous reports on bulk superconducting samples. AC calorimetry, however, does not show evidence for either bulk superconductivity or magnetism for pressures up to 1.6 GPa. Our results highlight the role of inhomogeneity in chemical-vapor-transport-grown UTe$_2$ samples and serve as a cautionary tale when probing electrical resistivity alone.

cond-mat.str-el↗

arXiv2024

Evidence for incommensurate antiferromagnetism in nonsymmorphic UPd$_{0.65}$Bi$_2$

The intersection between nonsymmorphic symmetry and electronic correlations has emerged as a platform for topological Kondo semimetallic states and unconventional spin textures. Here we report the synthesis of nonsymmorphic UPd$_{0.65}$Bi$_2$ single crystals and their structural, electronic, magnetic, and thermodynamic properties. UPd$_{0.65}$Bi$_2$ orders antiferromagnetically (AFM) below $T_N\simeq$ 161 K as evidenced by a sharp cusp in magnetic susceptibility, a second-order phase transition in specific heat, and an upturn in electrical resistivity, which suggests an incommensurate AFM structure that deviates from the A-type magnetism typically observed in this class of materials. Across $T_N$, Hall effect measurements reveal a change from electron-dominated to hole-dominated transport, which points to a sharp reconstruction in the electronic structure at $T_N$. Upon further cooling, a first-order transition is observed at $T_1 \simeq 30 $K in magnetic susceptibility and heat capacity but not in electrical resistivity or Hall measurements, which indicates a small change in the AFM structure that does not affect the electronic structure. Our specific heat data reveal a small Sommerfeld coefficient ($\gamma \simeq$13 mJmol$^{-1}$K$^{-2}$), consistent with localized 5$f$ electrons. Our results indicate that UPd$_{0.65}$Bi$_2$ hosts weak electronic correlations and is likely away from a Kondo semimetallic state. Low-temperature magnetization measurements show that the AFM structure is remarkably stable to 160 kOe and does not undergo any field-induced transitions. Neutron diffraction and magnetization experiments at higher fields would be valuable to probe the presence of unconventional spin textures.

cond-mat.str-el↗

arXiv2023

Evidence for charge delocalization crossover in the quantum critical superconductor CeRhIn$_5$

The nature of charge degrees-of-freedom distinguishes scenarios for interpreting the character of a second order magnetic transition at zero temperature, that is, a magnetic quantum critical point (QCP). Heavy-fermion systems are prototypes of this paradigm, and in those, the relevant question is where, relative to a magnetic QCP, does the Kondo effect delocalize their $f$-electron degrees-of-freedom. Herein, we use pressure-dependent Hall measurements to identify a finite-temperature scale $E_\text{loc}$ that signals a crossover from $f$-localized to $f$-delocalized character. As a function of pressure, $E_\text{loc}(P)$ extrapolates smoothly to zero temperature at the antiferromagnetic QCP of CeRhIn$_5$ where its Fermi surface reconstructs, hallmarks of Kondo-breakdown criticality that generates critical magnetic and charge fluctuations. In 4.4% Sn-doped CeRhIn$_5$, however, $E_\text{loc}(P)$ extrapolates into its magnetically ordered phase and is decoupled from the pressure-induced magnetic QCP, which implies a spin-density-wave (SDW) type of criticality that produces only critical fluctuations of the SDW order parameter. Our results demonstrate the importance of experimentally determining $E_\text{loc}$ to characterize quantum criticality and the associated consequences for understanding the pairing mechanism of superconductivity that reaches a maximum $T_\text{c}$ in both materials at their respective magnetic QCP.

cond-mat.str-el↗

arXiv2022

Interwoven atypical quantum states in CeLiBi$_2$

We report the discovery of CeLiBi$_2$, the first example of a material in the tetragonal Ce$TX_2$ ($T$ = transition metal; $X$ = pnictogen) family wherein an alkali cation replaces the typical transition metal. Magnetic susceptibility and neutron powder diffraction measurements are consistent with a crystal-field $Γ_6$ ground state Kramers doublet that orders antiferromagnetically below $T_N = 3.4$ K with an incommensurate propagation wave vector ${\bf{k}} = (0, 0.0724(4), 0.5)$ that generates a nanometric modulation of the magnetic structure. The best model of the ordered state is an elliptical cycloid with Ce moments primarily residing in the $ab$ plane. This is highly unusual, as all other $Γ_6$ Ce$TX_2$ members order ferromagnetically. Further, we observe an atypical hard-axis metamagnetic transition at $2$ T in magnetostriction, magnetization, and resistivity measurements. CeLiBi$_2$ is a rare example of a highly conductive material with dominant skew scattering leading to a large anomalous Hall effect. Quantum oscillations with five frequencies arise in magnetostriction and magnetic susceptibility data to $T = 30$ K and $μ_0H = 55$ T, which indicate small Fermi pockets of light carriers with effective masses as low as 0.07$m_e$. Density functional theory calculations indicate that square-net Dirac-like Bi$-p$ bands are responsible for these ultralight carriers. Together, our results show that CeLiBi$_2$ enables multiple atypical magnetic and electronic properties in a single clean material.

cond-mat.str-el↗

arXiv2022

Thermodynamic and electrical transport properties of UTe$_2$ under uniaxial stress

Despite intense experimental efforts, the nature of the unconventional superconducting order parameter of UTe$_2$ remains elusive. This puzzle stems from different reported numbers of superconducting transitions at ambient pressure, as well as a complex pressure-temperature phase diagram. To bring new insights into the superconducting properties of UTe$_2$, we measured the heat capacity and electrical resistivity of single crystals under compressive uniaxial stress $σ$ applied along different crystallographic directions. We find that the critical temperature $T_{\rm c}$ of the single observed bulk superconducting transition decreases with $σ$ along $[100]$ and $[110]$ but increases with $σ$ along $[001]$. Aside from its effect on $T_{\rm c}$, we notice that $c$-axis stress leads to a significant piezoresistivity, which we associate with the shift of the zero-pressure resistivity peak at $T^\star \approx 15\, \rm K$ to lower temperatures under stress. Finally, we show that an in-plane shear stress $σ_{xy}$ does not induce any observable splitting of the superconducting transition over a stress range of $σ_{xy}\approx 0.17 \, \rm GPa$. This result suggests that the superconducting order parameter of UTe$_2$ may be single-component at ambient pressure.

cond-mat.supr-con↗

arXiv2021

Robust narrow-gap semiconducting behavior in square-net La$_{3}$Cd$_{2}$As$_{6}$

ABSTRACT: Narrow-gap semiconductors are sought-after materials due to their potential for long-wavelength detectors, thermoelectrics, and more recently non-trivial topology. Here we report the synthesis and characterization of a new family of narrow-gap semiconductors, $R$$_{3}$Cd$_{2}$As$_{6}$ ($R=$ La, Ce). Single crystal x-ray diffraction at room temperature reveals that the As square nets distort and Cd vacancies order in a monoclinic superstructure. A putative charge-density ordered state sets in at 279~K in La$_{3}$Cd$_{2}$As$_{6}$ and at 136~K in Ce$_{3}$Cd$_{2}$As$_{6}$ and is accompanied by a substantial increase in the electrical resistivity in both compounds. The resistivity of the La member increases by thirteen orders of magnitude on cooling, which points to a remarkably clean semiconducting ground state. Our results suggest that light square net materials within a $I4/mmm$ parent structure are promising clean narrow-gap semiconductors.

cond-mat.mtrl-sci↗

arXiv2020

Localized-to-itinerant transition preceding antiferromagnetic quantum critical point and gapless superconductivity in CeRh$_{0.5}$Ir$_{0.5}$In$_5$

A fundamental problem posed from the study of correlated electron compounds, of which heavy-fermion systems are prototypes, is the need to understand the physics of states near a quantum critical point (QCP). At a QCP, magnetic order is suppressed continuously to zero temperature and unconventional superconductivity often appears. Here, we report pressure ($P$) -dependent $^{115}$In nuclear quadrupole resonance (NQR) measurements on heavy-fermion antiferromagnet CeRh$_{0.5}$Ir$_{0.5}$In$_5$. These experiments reveal an antiferromagnetic (AF) QCP at $P_{\rm c}^{\rm AF}$ = 1.2 GPa where a dome of superconductivity reaches a maximum transition temperature $T_{\rm c}$. Preceding $P_{\rm c}^{\rm AF}$, however, the NQR frequency $ν_{\rm Q}$ undergoes an abrupt increase at $P_{\rm c}^{\rm *}$ = 0.8 GPa in the zero-temperature limit, indicating a change from localized to itinerant character of cerium's $f$-electron and associated small-to-large change in the Fermi surface. At $P_{\rm c}^{\rm AF}$ where $T_{\rm c}$ is optimized, there is an unusually large fraction of gapless excitations well below $T_{\rm c}$ that implicates spin-singlet, odd-frequency pairing symmetry.

cond-mat.str-el↗

arXiv2020

Heavy-electron quantum criticality and single-particle spectroscopy

Angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) have become indispensable tools in the study of correlated quantum materials. Both probe complementary aspects of the single-particle excitation spectrum. Taken together, ARPES and STM have the potential to explore properties of the electronic Green's function, a central object of many-body theory. This review explicates this potential with a focus on heavy-electron quantum criticality, especially the role of Kondo destruction. A discussion on how to probe the Kondo destruction effect across the quantum-critical point using ARPES and STM measurements is presented. Particular emphasis is placed on the question of how to distinguish between the signatures of the initial onset of hybridization-gap formation, which is the "high-energy" physics to be expected in all heavy-electron systems, and those of Kondo destruction, which characterizes the low-energy physics and, hence, the nature of quantum criticality. Recent progress and possible challenges in the experimental investigations are surveyed, the STM and ARPES spectra for several quantum-critical heavy-electron compounds are compared, and the prospects for further advances are outlined.

cond-mat.str-el↗

arXiv2019

Crystal electric field splitting and f-electron hybridization in heavy fermion CePt2In7

We use high-resolution angle-resolved photoemission spectroscopy to investigate the electronic structure of the antiferromagnetic heavy fermion compound CePt2In7, which is a member of the CeIn3-derived heavy fermion material family. Weak hybridization among 4f electron states and conduction bands was identified in CePt2In7 at low temperature much weaker than that in the other heavy fermion compounds like CeIrIn5 and CeRhIn5. The Ce 4f spectrum shows fine structures near the Fermi energy, reflecting the crystal electric field splitting of the 4f^1_5/2 and 4f^1_7/2 states. Also, we find that the Fermi surface has a strongly three-dimensional topology, in agreement with density-functional theory calculations.

cond-mat.str-el↗

arXiv2019

Tunable quantum critical point and detached superconductivity in Al-doped CrAs

The origin of unconventional superconductivity and its relationship to a T=0 K continuous quantum phase transition (a quantum critical point, QCP), which is hidden inside the dome of a superconducting state, have long been an outstanding puzzle in correlated superconductors. The observation and tuning of the hidden QCP, which is critical in resolving the mystery, however, has been rarely reported due to lack of ideal systems. The helical antiferromagnet CrAs provides an example in which a dome of superconductivity appears at a pressure where its magnetic transition goes to zero temperature. Here we report the tuning of a projected critical point in CrAs via Al chemical doping (Al-CrAs) and separation of the magnetic critical point from the pressure-induced superconducting phase. When CrAs is doped with Al, its AFM ordering temperature TN increases from 260 K to 270 K. With applied pressure, TN decreases and extrapolates to zero Kelvin near 4.5 kbar, which is shifted from 8 kbar for undoped CrAs. A funnel of anomalously enhanced electron scattering and a non-Fermi liquid resistivity underscore an AFM QCP near 4.5 kbar in Al-CrAs. Pressure-induced superconductivity, in contrast, is almost independent of Al doping and forms a dome with essentially the identical maximum Tc and same optimal pressure as in pure CrAs. The clear separation between the tuned AFM QCP and Tc maximum in Al-CrAs suggests that superconductivity is independent of the AFM QCP, illustrating subtleties in the interplay between superconductivity and quantum criticality in correlated electron systems.

cond-mat.supr-con↗

arXiv2018

Imaging the magnetic states in an actinide ferromagnet UMn$_2$Ge$_2$

We present studies of the magnetic domain structure of UMn$_2$Ge$_2$ single crystals using a home-built low temperature magnetic force microscope. The material has two distinct magnetic ordering temperatures, originating from the Mn and U moments. At room temperature, where the Mn moments dominate, there are flower-like domain patterns similar to those observed in uniaxial ferromagnets. After exposing the sample to a one-tesla magnetic field near 40 K, the evolution of the magnetic domains are imaged through zero-field warming up to 200 K. Near the ordering temperature of the uranium moments a clear change in the domain wall motion is observed. The domain size analysis of the flower-like pattern reveals that the domain structure is consistent with a model of branching domains.

cond-mat.mtrl-sci↗

arXiv2016

Conducting interface in oxide homojunction: understanding of superior properties in black TiO2

Black TiO2 nanoparticles with a crystalline-core and amorphous-shell structure exhibit superior optoelectronic properties in comparison with pristine TiO2. The fundamental mechanisms underlying these enhancements, however, remain unclear, largely due to the inherent complexities and limitations of powder materials. Here, we fabricate TiO2 homojunction films consisting of an oxygen-deficient amorphous layer on top of a highly crystalline layer, to simulate the structural/functional configuration of black TiO2 nanoparticles. Metallic conduction is achieved at the crystalline-amorphous homointerface via electronic interface reconstruction, which we show to be the main reason for the superior properties of black TiO2. This work not only achieves an unprecedented understanding of black TiO2, but also provides a new perspective for investigating carrier generation and transport behavior at oxide interfaces, which are of tremendous fundamental and technological interest.

cond-mat.mtrl-sci↗

arXiv2016

Quasiparticle interference of heavy fermions in resonant X-ray scattering

Resonant X-ray scattering (RXS) has recently become an increasingly important tool for the study of ordering phenomena in correlated electron systems. Yet, the interpretation of the RXS experiments remains theoretically challenging due to the complexity of the RXS cross-section. Central to this debate is the recent proposal that impurity-induced Friedel oscillations, akin to quasiparticle interference signals observed with the scanning tunneling microscope (STM), can lead to scattering peaks in the RXS experiments. The possibility that quasiparticle properties can be probed in RXS measurements opens up a new avenue to study the bulk band structure of materials with the orbital and element selectivity provided by RXS. Here, we test these ideas by combining RXS and STM measurements of the heavy fermion compound CeMIn$_5$ (M = Co, Rh). Temperature and doping dependent RXS measurements at the Ce-M$_4$ edge show a broad scattering enhancement that correlates with the appearance of heavy f-electron bands in these compounds. The scattering enhancement is consistent with the measured quasiparticle interference signal in the STM measurements, indicating that quasiparticle interference can be probed through the momentum distribution of RXS signals. Overall, our experiments demonstrate new opportunities for studies of correlated electronic systems using the RXS technique.

cond-mat.str-el↗

arXiv2016

Superconductivity in CaBi$_{2}$

Superconductivity is observed with critical temperature $T_{c}$ = 2.0 K in self-flux-grown single crystals of $CaBi_{2}$. This material adopts the $ZrSi_{2}$ structure type with lattice parameters a = 4.696(1) $Å$, b = 7.081(2) $Å$ and c = 4.611(1) $Å$. The crystals of $CaBi_{2}$ were studied by means of magnetic susceptibility, specific heat and electrical resistivity measurements. The heat capacity jump at $T_{c}$ is $ΔC/γT_{c}$ = 1.41, confirming bulk superconductivity; the Sommerfeld coefficient $γ$ = 4.1 $mJ\: mol^{-1}\, K^{-2}$ and the Debye temperature $Θ_{D}$ = 157 K. The electron-phonon coupling strength is $λ_{el-ph}$ = 0.59, and the thermodynamic critical field $H_{c}$ is low, between 111 and 124 Oe $CaBi_{2}$ is a moderate coupling type-I superconductor. Results of electronic structure calculations are reported and charge densities, electronic bands, densities of states and Fermi surfaces are discussed, focusing on the effects of spin\textendash orbit coupling and electronic property anisotropy. We find a mixed quasi-2D + 3D character in the electronic structure, which reflects the layered crystal structure of the material.

cond-mat.supr-con↗

arXiv2014

Switching of magnetic domains reveals evidence for spatially inhomogeneous superconductivity

The interplay of magnetic and charge fluctuations can lead to quantum phases with exceptional electronic properties. A case in point is magnetically-driven superconductivity, where magnetic correlations fundamentally affect the underlying symmetry and generate new physical properties. The superconducting wave-function in most known magnetic superconductors does not break translational symmetry. However, it has been predicted that modulated triplet p-wave superconductivity occurs in singlet d-wave superconductors with spin-density wave (SDW) order. Here we report evidence for the presence of a spatially inhomogeneous p-wave Cooper pair-density wave (PDW) in CeCoIn5. We show that the SDW domains can be switched completely by a tiny change of the magnetic field direction, which is naturally explained by the presence of triplet superconductivity. Further, the Q-phase emerges in a common magneto-superconducting quantum critical point. The Q-phase of CeCoIn5 thus represents an example where spatially modulated superconductivity is associated with SDW order.

cond-mat.supr-con↗