arXiv subjects

Qiaozhi Xu

Publications and source records attributed to Qiaozhi Xu.

4 recordsLinked to original sources

arXiv2025

Observation of a spin-textured nematic Kondo lattice

The Kondo lattice mode, as one of the most fundamental models in condensed matter physics, has been employed to describe a wide range of quantum materials such as heavy fermions, transition metal dichalcogenides and two-dimensional Moire systems. Discovering new phases on Kondo lattice and unveiling their mechanisms are crucial to the understanding of strongly correlated systems. Here, in a layered Kondo magnet USbTe, we observe a spin-textured nematic state and visualize a heavy electronic liquid-crystal phase. Employing scanning tunneling microscopy and spectroscopy (STM/STS), we visualize a tetragonal symmetry breaking of heavy electronic states around the Fermi level. Through systematically investigating the temperature and energy dependence of spectroscopic data, we find that the nematic state coincides with the formation of heavy quasi-particles driven by band hybridization. Remarkably, using spin polarized STM, we demonstrate that the nematic state is spin polarized, which not only suggests its intrinsically electronic nature, but also represents the unique magnetic texture of nematic heavy fermions. Our findings unveil a novel correlation-mediated order whose mechanism is inherently tied to Kondo-lattice physics. The observation of heavy nematic states enriches the phase diagram of correlated systems and provides a rare platform to explore the interplay of Kondo physics, spontaneous symmetry breaking and quantum criticality.

cond-mat.str-el↗

arXiv2025

High temperature surface state in Kondo insulator U$_3$Bi$_4$Ni$_3$

The resurgence of interest in Kondo insulators has been driven by two major mysteries: the presence of metallic surface states and the observation of quantum oscillations. To further explore these mysteries, it is crucial to investigate another similar system beyond the two existing ones, SmB$_6$ and YbB$_{12}$. Here, we address this by reporting on a Kondo insulator, U$_3$Bi$_4$Ni$_3$. Our transport measurements reveal that a surface state emerges below 250 K and dominates transport properties below 150 K, which is well above the temperature scale of SmB$_6$ and YbB$_{12}$. At low temperatures, the surface conductivity is about one order of magnitude higher than the bulk. The robustness of the surface state indicates that it is inherently protected. The similarities and differences between U$_3$Bi$_4$Ni$_3$ and the other two Kondo insulators will provide valuable insights into the nature of metallic surface states in Kondo insulators and their interplay with strong electron correlations.

cond-mat.str-el↗

arXiv2025

Quantum noise spectroscopy of superconducting dynamics in thin film Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$

Characterizing the low-energy dynamics of quantum materials is crucial to our understanding of strongly correlated electronic states. Yet, it remains experimentally challenging to investigate such dynamics with high spectroscopic resolution in both frequency and momentum space, particularly in two-dimensional correlated systems. Here, we leverage Nitrogen-Vacancy (NV) centers in diamond as a powerful and non-invasive tool to study thin-film Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (BSCCO), revealing several distinct dynamical phenomena across the superconducting phase diagram. At zero magnetic field and low temperatures, NV depolarization ($T_1$) noise spectroscopy captures the low-frequency (GHz-scale) magnetic noise generated by nodal superconducting quasiparticle excitations, in agreement with Bardeen-Cooper-Schrieffer (BCS) mean-field theory. Near the critical temperature $T_c \approx 90$ K, supercurrent-fluctuation-induced noise leads to a sharp reduction of the NV $T_1$. By carefully analyzing the temperature-scaling of $T_1$, we observe clear deviations from the BCS prediction, reflecting the importance of order parameter fluctuations and enabling the determination of both static and dynamical critical exponents. When a small field is applied, we detect a broad and asymmetric reduction of NV $T_1$ near $T_c$; the field-induced smearing of the transition unveils the presence of a vortex liquid phase. Finally, NV decoherence ($T_2$) noise spectroscopy allows us to characterize magnetic noise at even lower MHz-scale frequencies and obtain evidence for complex vortex-solid fluctuations well below $T_c$. Our results establish quantum noise spectroscopy as a versatile platform for probing dynamical phenomena in superconductors, with frequency and length scales complementary to existing techniques.

cond-mat.supr-con↗

arXiv2024

Tunable Giant Anomalous Hall in a Kondo Lattice Ferromagnet UBiTe

Kondo lattice systems are recognized for potentially hosting a variety of rich topological phases. Several pioneering studies have demonstrated significant anomalous Hall and anomalous Nernst effects in these systems, attributed to the Berry curvature of the hybridization bands. In this study, we investigate UBiTe, a ferromagnetic Kondo lattice system. Our findings reveal that the intrinsic contribution to the anomalous Hall conductivity is closely tied to the Kondo coherence temperature. Moreover, we demonstrate that slight shifts in the Fermi level across three different samples significantly influence this intrinsic contribution, in alignment with the Berry curvature localized within the narrow hybridization bands. This provides a stark contrast to the less pronounced sensitivity observed in weakly correlated Weyl semimetals, underscoring the distinctive electronic properties of Kondo lattice systems. The anomalous Hall conductivity of one samples ranks among the highest reported for topological magnetic materials.

cond-mat.str-el↗