arXiv subjects

P. J. Sun

Publications and source records attributed to P. J. Sun.

4 recordsLinked to original sources

arXiv2025

Weyl Fermion Manipulation through Magnetic Transitions in the Ferromagnetic Non-Centrosymmetric Weyl semimetal PrAlSi

PrAlSi, a non-centrosymmetric ferromagnetic Weyl semimetal candidate with a Curie temperature of 17.8K, offers a unique platform for exploring the interplay of symmetry breaking and topological electronic structures. Up to now, the Weyl fermion distribution as well as their evolution across the ferromagnetic to paramagnetic phase transition in PrAlSi has not been explored. Here, we uncover the presence of Weyl fermions in PrAlSi and demonstrate they could be manipulated through the magnetic phase transition. Our ab-initio calculations indicate a shift in the momentum and energy positions of Weyl fermions, alongside an increase in Weyl point numbers due to band splitting. The predicted band splitting and shifting of Weyl fermions are corroborated by our angle-resolved photoemission spectroscopy experiments. Such manipulation of Weyl fermions leads to the appearance of a net chirality charge and a significant modulation in optical conductivity, as proposed by our calculations. Our research presents a novel method for adjusting the properties of Weyl semimetals by controlling Weyl fermions through magnetic phase transitions, positioning PrAlSi as a model system.

cond-mat.mtrl-sci↗

arXiv2024

Band structure reconstruction in the topological semimetal PrAlSi

The interplay between nontrivial topology, magnetism and strong correlation has generated considerable research interest in condensed matter physics. The topological RAlX (R = rare earth ; X = Si and Ge) family has provided an excellent platform for exploring these complex interactions. Here, we performed infrared spectroscopy measurements on the ferromagnetic (FM) topological semimetal PrAlSi, in oder to investigate the impact of FM orderings on the topological band structure. We find that the optical conductivity associated with the Dirac/Weyl cones exhibits two segments of linearly increasing parts in the normal state, connected by a kink feature at around 1 960 cm-1. By entering the FM state, however, an additional linear-growing segment shows up in between the original ones, suggesting that the band structure is reconstructed. We propose that these observations can be effectively explained by a scenario where the Dirac/Weyl nodes are split into pairs of Weyl nodes with lower degeneracy, due to the time reversal symmetry breaking induced by the FM ordering. This band structure reconstruction also leads to a sudden enhancement of the itinerant carrier density. In addition, the effective mass of the itinerant carriers are estimated to be two orders of magnitude smaller than the free electron mass, providing a rare case where nearly all the free carriers exhibit behaviors characteristic of relativistic Dirac or Weyl fermions. Our results demonstrate an compelling example of the strong interaction between magnetic order and topological band structures, which opens up new avenues for exploring novel topological materials and their potential applications.

physics.optics↗

arXiv2022

CeCu$_{2}$Si$_{2}$ and YbRh$_{2}$Si$_{2}$: Strange Cases of Heavy-Fermion Superconductivity

The heavy-fermion superconductor CeCu$_{2}$Si$_{2}$ exhibits two-band, $d$-wave superconductivity with a finite energy gap over the whole Fermi surface around the magnetic instability where 4$f$ antiferrerromagnetic order is suppressed. In contrast, in YbRh$_{2}$Si$_{2}$ heavy-fermion superconductivity appears only when 4$f$-electronic antiferromagnetic order is replaced at ultra-low temperatures by a combined nuclear and 4$f$-spin order. Whereas both compounds exhibit different variants of antiferromagnetic instabilities, i.e., a spin-density-wave quantum critical point in CeCu$_{2}$Si$_{2}$ and one of "partial-Mott" type in YbRh$_{2}$Si$_{2}$, in both cases the Cooper pairing, as well as the pronounced "strange-metal" behavior in YbRh$_{2}$Si$_{2}$, appear to be driven by large-to-small Fermi surface fluctuations. The transport properties and scanning tunneling spectroscopy (STS) for these materials are dominated by single-ion Kondo scatterings down to very low temperatures. Further open problems of the Kondo lattice include both the interplay between superconductivity and antiferromagnetic order as well as the onset of lattice coherence. While microscopic coexistence of superconductivity and antiferromagnetism seems to require a sufficiently large staggered moment, the onset of lattice coherence in transport measurements and STS is associated solely with the crystal-field-doublet ground state, while it involves the fully degenerate Hund's rule multiplet in ARPES.

cond-mat.supr-con↗

arXiv2019

Evolution of Magnetic Double Helix and Quantum Criticality near a Dome of Superconductivity in CrAs

At ambient pressure CrAs undergoes a first-order transition into a double-helical magnetic state at TN = 265 K, which is accompanied by a structural transition. The recent discovery of pressure-induced superconductivity in CrAs makes it important to clarify the nature of quantum phase transitions out of its coupled structural/helimagnetic order. Here we show, via neutron diffraction on the single-crystal CrAs under hydrostatic pressure (P), that the combined order is suppressed at Pc ~ 10 kbar, near which bulk superconductivity develops with a maximal transition temperature Tc ~ 2 K. We further show that the coupled order is also completely suppressed by phosphorus doping in CrAs1-xPx at a critical xc ~ 0.05, above which inelastic neutron scattering evidenced persistent antiferromagnetic correlations, providing a possible link between magnetism and superconductivity. In line with the presence of antiferromagnetic fluctuations near Pc (xc), the A coefficient of the quadratic temperature dependence of resistivity exhibits a dramatic enhancement as P (x) approaches Pc (xc), around which Res(T) has a non-Fermi-liquid form. Accordingly, the electronic specific-heat coefficient of CrAs1-xPx peaks out around xc. These properties provide clear evidences for quantum criticality, which we interpret as originating from a nearly second-order helimagnetic quantum phase transition that is concomitant with a first-order structural transition. Our findings in CrAs highlight the distinct characteristics of quantum criticality in bad metals, thereby bringing out new insights into the physics of unconventional superconductivity such as occurring in the high-Tc iron pnictides.

cond-mat.supr-con↗