arXiv subjects

Liqin Yan

Publications and source records attributed to Liqin Yan.

8 recordsLinked to original sources

arXiv2025

Sub-spin-flop switching of a fully compensated antiferromagnet by magnetic field

The control of antiferromagnets by magnetic fields represents a fundamental challenge in condensed matter physics, owing to their fully compensated magnetic order and vanishing net magnetization. Conventional methods rely on either uncompensated moments or high-field spin-flop transitions. Here, we demonstrate low-field switching in the fully compensated antiferromagnet CeNiAsO -- a material recently proposed as a candidate for $p$-wave magnetism. Using an in-plane magnetic field well below the spin-flop threshold, we selectively stabilize one of two degenerate antiferromagnetic domains with mutually orthogonal sublattice orientations. This field-induced domain selection allows reversible and nonvolatile switching of a giant in-plane resistivity anisotropy up to $\sim35\,\%$ -- a magnitude that far exceeds conventional anisotropy signals driven by spin-orbit coupling. The switching behavior persists across both the low-temperature noncollinear N\'{e}el phase and the higher-temperature collinear spin-density-wave phase, highlighting the universality of the domain-selection mechanism. Our work establishes a practical approach for manipulating compensated antiferromagnets with modest magnetic fields and underscores their potential for high-performance spintronic devices based on giant and switchable resistivity anisotropy.

cond-mat.mes-hall↗

arXiv2024

Magnetic ground states in kagome YCu$_3$(OH)$_6$[(Cl$_x$Br$_{1-x}$)$_{3-y}$(OH)$_{y}$]

Quantum spin liquids represent exotic states of spin systems characterized by long-range entanglement and emergent fractionalized quasiparticles. It is generally believed that disorder is hostile to quantum spin liquids. In our study, we investigated the magnetic properties of a kagome system, YCu$_3$(OH)$_6$[(Cl$_x$Br$_{1-x}$)$_{3-y}$(OH)$_{y}$]. Within this system, some of the hexagons exhibit alternate bonds along the Cu-O-Cu exchange paths, while others remain uniform. We found that a long-range antiferromagnetic order emerges when uniform hexagons dominate. Conversely, a possible quantum-spin-liquid state arises when the number of alternate-bond hexagons exceeds about 2/3. Therefore, the alternate-bond hexagons, typically considered as disorders, actually serve as the building blocks of the quantum spin liquid in this system. Notably, the low-temperature properties of the quantum spin liquid are directly associated with the height of the out-of-plane yttrium ions, which may be linked to changes in superexchange energies. Our results suggest that understanding the magnetic ground states in this system lies beyond the theoretical framework of the Heisenberg model constructed on the kagome lattice.

cond-mat.str-el↗

arXiv2016

Nonvolatile Multi-level Memory and Boolean Logic Gates Based on a Single Memtranstor

Memtranstor that correlates charge and magnetic flux via nonlinear magnetoelectric effects has a great potential in developing next-generation nonvolatile devices. In addition to multi-level nonvolatile memory, we demonstrate here that nonvolatile logic gates such as NOR and NAND can be implemented in a single memtranstor made of the Ni/PMN-PT/Ni heterostructure. After applying two sequent voltage pulses (X1, X2) as the logic inputs on the memtranstor, the output magnetoelectric voltage can be positive high (logic "1"), positive low (logic "0"), or negative (logic "0"), depending on the levels of X1 and X2. The underlying physical mechanism is related to the complete or partial reversal of ferroelectric polarization controlled by inputting selective voltage pulses, which determines the magnitude and sign of the magnetoelectric voltage coefficient. The combined functions of both memory and logic could enable the memtranstor as a promising candidate for future computing systems beyond von Neumann architecture.

cs.ET↗

arXiv2013

Giant exchange bias in a single-phase magnet with two magnetic sublattices

Exchange bias phenomenon is generally ascribed to the exchange coupling at the interfaces between ferromagnetic and antiferromagnetic layers. Here, we propose a bulk form of exchange bias in a single-phase magnet where the coupling between two magnetic sublattices induces a significant shift of the coercive field after a field cooling. Our experiments in a complicated magnet YbFe2O4 demonstrate a giant exchange bias at low temperature when the coupling between the Yb3+ and Fe2+/Fe3+ sublattices take places. The cooling magnetic field dependence and the training effect of exchange bias are consistent with our model. In strong contrast to conventional interfacial exchange bias, this bulk form of exchange bias can be huge, reaching the order of a few Tesla.

cond-mat.str-el↗

arXiv2010

Evidence of a universal and isotropic 2Δ/kBTC ratio in 122-type iron pnictide superconductors over a wide doping range

We have systematically investigated the doping and the directional dependence of the gap structure in the 122-type iron pnictide superconductors by point contact Andreev reflection spectroscopy. The studies were performed on single crystals of Ba1-xKxFe2As2 (x = 0.29, 0.49, and 0.77) and SrFe1.74Co0.26As2 with a sharp tip of Pb or Au pressed along the c-axis or the ab-plane direction. The conductance spectra obtained on highly transparent contacts clearly show evidence of a robust superconducting gap. The normalized curves can be well described by the Blonder-Tinkham-Klapwijk model with a lifetime broadening. The determined gap value scales very well with the transition temperature, giving the 2Δ/kBTC value of ~ 3.1. The results suggest the presence of a universal coupling behavior in this class of iron pnictides over a broad doping range and independent of the sign of the doping. Moreover, conductance spectra obtained on c-axis junctions and ab-plane junctions indicate that the observed gap is isotropic in these superconductors.

cond-mat.supr-con↗

arXiv2009

Josephson effect between electron-doped and hole-doped iron pnictide single crystals

We have observed the Josephson effect in junctions formed between single crystals of SrFe1.74Co0.26As2 and Ba0.23K0.77Fe2As2. I-V curves showed resistively-shunted junction characteristics, and the ac Josephson effect was observed under microwave irradiation. By applying an in-plane magnetic field, the critical current is completely modulated and shows a relatively symmetric diffraction pattern, consistent with the intermediate junction limit. The observation of the Josephson effect in the p-n bicrystal structure not only has significant implications for designing phase-sensitive junctions to probe the pairing symmetry of iron pnictide superconductors, but also represents an important step in developing all iron pnictide devices for applications.

cond-mat.supr-con↗

arXiv2009

Observation of the Josephson effect in Pb/(Ba,K)Fe2As2 single crystal junctions

We have fabricated c-axis Josephson junctions on single crystals of (Ba,K)Fe2As2 by using Pb as the counter electrode in two geometries, planar and point contact. Junctions in both geometries show resistively shunted junction I-V curves below the Tc of the counter electrode. Microwave induced steps were observed in the I-V curves, and the critical currents are suppressed with an in-plane magnetic field in a manner consistent with the small junction limit. ICRN products of up to 0.3 mV have been observed in these junctions at 4.2 K. The observation of Josephson coupling along the c-axis between (Ba,K)Fe2As2 and a conventional superconductor suggests the existence of a s-wave superconducting order parameter in this class of iron pnictide superconductors.

cond-mat.supr-con↗

arXiv2008

Evidence for Coexistence of Superconductivity and Magnetism in Single Crystals of Co-doped SrFe$_2$As$_2$

In order to investigate whether magnetism and superconductivity coexist in Co-doped SrFe$_2$As$_2$, we have prepared single crystals of SrFe$_{2-x}$Co$_x$As$_2$, $x$ = 0 and 0.4, and characterized them via X-ray diffraction, electrical resistivity in zero and applied field up to 9 T as well as at ambient and applied pressure up to 1.6 GPa, and magnetic susceptibility. At $x$ = 0.4, there is both magnetic and resistive evidence for a spin density wave transition at 120 K, while $T_c$ = 19.5 K - indicating coexistent magnetism and superconductivity. A discussion of how these results compare with reported results, both in SrFe$_{2-x}$Co$_x$As$_2$ and in other doped 122 compounds, is given.

cond-mat.supr-con↗