arXiv subjects

Jing Xia

Publications and source records attributed to Jing Xia.

At least 91 records · Page 5Linked to original sources

arXiv2017

A microwave field-driven transistor-like skyrmionic device with the microwave current-assisted skyrmion creation

Magnetic skyrmion is a topologically protected domain-wall structure at nanoscale, which could serve as a basic building block for advanced spintronic devices. Here, we propose a microwave field-driven skyrmionic device with the transistor-like function, where the motion of a skyrmion in a voltage-gated ferromagnetic nanotrack is studied by micromagnetic simulations. It is demonstrated that the microwave field can drive the motion of a skyrmion by exciting propagating spin waves, and the skyrmion motion can be governed by a gate voltage. We also investigate the microwave current-assisted creation of a skyrmion to facilitate the operation of the transistor-like skyrmionic device on the source terminal. It is found that the microwave current with an appropriate frequency can reduce the threshold current density required for the creation of a skyrmion from the ferromagnetic background. The proposed transistor-like skyrmionic device operated with the microwave field and current could be useful for building future skyrmion-based circuits.

cond-mat.mes-hall↗

arXiv2017

Controllable transport of a skyrmion in a ferromagnetic narrow channel with voltage-controlled magnetic anisotropy

Magnetic skyrmions have potential applications in next-generation spintronics devices with ultralow energy consumption. In this work, the current-driven skyrmion motion in a narrow ferromagnetic nanotrack with voltage-controlled magnetic anisotropy (VCMA) is studied numerically. By utilizing the VCMA effect, the transport of skyrmion can be unidirectional in the nanotrack, leading to a one-way information channel. The trajectory of the skyrmion can also be modulated by periodically located VCMA gates, which protects the skyrmion from destruction by touching the track edge. In addition, the location of the skyrmion can be controlled by adjusting the driving pulse length in the presence of the VCMA effect. Our results provide guidelines for practical realization of the skyrmion-based information channel, diode, and racetrack memory.

cond-mat.mes-hall↗

arXiv2017

Motion of skyrmions in nanowires driven by magnonic momentum-transfer forces

We study the motion of magnetic skyrmions in a nanowire induced by a spin-wave current $J$ flowing out of a driving layer close to the edge of the wire. By applying micromagnetic simulation and an analysis of the effective Thiele equation, we find that the skyrmion trajectory is governed by an interplay of both forces due to the magnon current and the wire boundary. The skyrmion is attracted to the driving layer and is accelerated by the repulsive force due to the wire boundary. We consider both cases of a driving longitudinal and transverse to the nanowire, but a steady-state motion of the skyrmion is only obtained for a transverse magnon current. For the latter case, we find in the limit of low current densities $J$ the velocity-current relation $v \sim J/α$ where $v$ is the skyrmion velocity and $α$ is the Gilbert damping. For large $J$ in case of strong driving, the skyrmion is pushed into the driving layer resulting in a drop of the skyrmion velocity and, eventually, the destruction of the skyrmion.

cond-mat.mes-hall↗

arXiv2017

Discovery of intrinsic ferromagnetism in 2D van der Waals crystals

It has been long hoped that the realization of long-range ferromagnetic order in two-dimensional (2D) van der Waals (vdW) crystals, combined with their rich electronic and optical properties, would open up new possibilities for magnetic, magnetoelectric and magneto-optic applications. However, in 2D systems, the long-range magnetic order is strongly hampered by thermal fluctuations which may be counteracted by magnetic anisotropy, according to the Mermin-Wagner theorem. Prior efforts via defect and composition engineering, and proximity effect only locally or extrinsically introduce magnetic responses. Here we report the first experimental discovery of intrinsic long-range ferromagnetic order in pristine Cr2Ge2Te6 atomic layers by scanning magneto-optic Kerr microscopy. In such a 2D vdW soft ferromagnet, for the first time, an unprecedented control of transition temperature of ~ 35% - 57% enhancement is realized via surprisingly small fields (<= 0.3 Tesla in this work), in stark contrast to the stiffness of the transition temperature to magnetic fields in the three-dimensional regime. We found that the small applied field enables an effective anisotropy far surpassing the tiny magnetocrystalline anisotropy, opening up a sizable spin wave excitation gap. Confirmed by renormalized spin wave theory, we explain the phenomenon and conclude that the unusual field dependence of transition temperature constitutes a hallmark of 2D soft ferromagnetic vdW crystals. Our discovery of 2D soft ferromagnetic Cr2Ge2Te6 presents a close-to-ideal 2D Heisenberg ferromagnet for studying fundamental spin behaviors, and opens the door for exploring new applications such as ultra-compact spintronics.

cond-mat.mes-hall↗

arXiv2017

Time-Reversal-Symmetry-Breaking Superconductivity in Epitaxial Bismuth/Nickel Bilayers

Superconductivity that spontaneously breaks time-reversal symmetry (TRS) has been found, so far, only in a handful of 3D crystals with bulk inversion symmetry. Here we report an observation of spontaneous TRS breaking in a 2D superconducting system without inversion symmetry: the epitaxial bilayer films of bismuth and nickel. The evidence comes from the onset of the polar Kerr effect at the superconducting transition in the absence of an external magnetic field, detected by the ultrasensitive loop-less fiber-optic Sagnac interferometer. Because of strong spin-orbit interaction and lack of inversion symmetry in a Bi/Ni bilayer, superconducting pairing cannot be classified as singlet or triplet. We propose a theoretical model where magnetic fluctuations in Ni induce superconducting pairing of the dxy = +- idx^2y^2 orbital symmetry between the electrons in Bi. In this model the order parameter spontaneously breaks the TRS and has a non-zero phase winding number around the Fermi surface, thus making it a rare example of a 2D topological superconductor.

cond-mat.supr-con↗

arXiv2017

Thickness dependent properties in oxide heterostructures driven by structurally induced metal-oxygen hybridization variations

Thickness driven electronic phase transitions are broadly observed in different types of functional perovskite heterostructures. However, uncertainty remains whether these effects are solely due to spatial confinement, broken symmetry or rather to a change of structure with varying film thickness. Here, we present direct evidence for the relaxation of oxygen 2p and Mn 3d orbital (p-d) hybridization coupled to the layer dependent octahedral tilts within a La2/3Sr1/3MnO3 film driven by interfacial octahedral coupling. An enhanced Curie temperature is achieved by reducing the octahedral tilting via interface structure engineering. Atomically resolved lattice, electronic and magnetic structures together with X-ray absorption spectroscopy demonstrate the central role of thickness dependent p-d hybridization in the widely observed dimensionality effects present in correlated oxide heterostructures.

cond-mat.mtrl-sci↗

arXiv2016

Magnetic Skyrmion Transport in a Nanotrack With Spatially Varying Damping and Non-adiabatic Torque

Reliable transport of magnetic skyrmions is required for any future skyrmion-based information processing devices. Here we present a micromagnetic study of the in-plane current-driven motion of a skyrmion in a ferromagnetic nanotrack with spatially sinusoidally varying Gilbert damping and/or non-adiabatic spin-transfer torque coefficients. It is found that the skyrmion moves in a sinusoidal pattern as a result of the spatially varying Gilbert damping and/or non-adiabatic spin-transfer torque in the nanotrack, which could prevent the destruction of the skyrmion caused by the skyrmion Hall effect. The results provide a guide for designing and developing the skyrmion transport channel in skyrmion-based spintronic applications.

cond-mat.mes-hall↗

arXiv2016

Control and manipulation of a magnetic skyrmionium in nanostructures

A magnetic skyrmionium is a nontopological soliton, which has a doughnut-like out-of-plane spin texture in thin films, and can be phenomenologically viewed as a coalition of two topological magnetic skyrmions with opposite topological numbers. Due to its zero topological number ($Q=0$) and doughnut-like structure, the skyrmionium has its distinctive characteristics as compared to the skyrmion with $Q=\pm 1$. Here we systematically study the generation, manipulation and motion of a skyrmionium in ultrathin magnetic nanostructures by applying a magnetic field or a spin-polarized current. It is found that the skyrmionium moves faster than the skyrmion when they are driven by the out-of-plane current, and their velocity difference is proportional to the driving force. However, the skyrmionium and skyrmion exhibit an identical current-velocity relation when they are driven by the in-plane current. It is also found that a moving skyrmionium is less deformed in the current-in-plane geometry compared with the skyrmionum in the current-perpendicular-to-plane geometry. Furthermore we demonstrate the transformation of a skyrmionium with $Q=0$ into two skyrmions with $Q=+1$ in a nanotrack driven by a spin-polarized current, which can be seen as the unzipping process of a skyrmionium. We illustrate the energy and spin structure variations during the skyrmionium unzipping process, where linear relations between the spin structure and energies are found. These results could have technological implications in the emerging field of skyrmionics.

cond-mat.mes-hall↗

arXiv2016

Chiral Majorana edge state in a quantum anomalous Hall insulator-superconductor structure

After the recognition of the possibility to implement Majorana fermions using the building blocks of solid-state matters, the detection of this peculiar particle has been an intense focus of research. Here we experimentally demonstrate a collection of Majorana fermions living in a one-dimensional transport channel at the boundary of a superconducting quantum anomalous Hall insulator thin film. A series of topological phase changes are controlled by the reversal of the magnetization, where a half-integer quantized conductance plateau (0.5e2/h) is observed as a clear signature of the Majorana phase. This transport signature can be well repeated during many magnetic reversal sweeps, and can be tracked at different temperatures, providing a promising evidence of the chiral Majorana edge modes in the system.

cond-mat.supr-con↗

arXiv2016

Spin-Cherenkov effect in a magnetic nanostrip with interfacial Dzyaloshinskii-Moriya interaction

Spin-Cherenkov effect enables strong excitations of spin waves (SWs) with nonlinear wave dispersions. The Dzyaloshinskii-Moriya interaction (DMI) results in anisotropy and nonreciprocity of SWs propagation. In this work, we study the effect of the interfacial DMI on SW Cherenkov excitations in permalloy thin-film strips within the framework of micromagnetism. By performing micromagnetic simulations, it is shown that coherent SWs are excited when the velocity of a moving magnetic source exceeds the propagation velocity of the SWs. Moreover, the threshold velocity of the moving magnetic source with finite DMI can be reduced compared to the case of zero DMI. It thereby provides a promising route towards efficient SW generation and propagation, with potential applications in spintronic and magnonic devices.

cond-mat.mes-hall↗

arXiv2015

Topological Kondo Insulators

This article reviews recent theoretical and experimental work on a new class of topological material - topological Kondo insulators, which develop through the interplay of strong correlations and spin-orbit interactions. The history of Kondo insulators is reviewed along with the theoretical models used to describe these heavy fermion compounds. The Fu-Kane method of topological classification of insulators is used to show that hybridization between the conduction electrons and localized f-electrons in these systems gives rise to interaction-induced topological insulating behavior. Finally, some recent experimental results are discussed, which appear to confirm the theoretical prediction of the topological insulating behavior in Samarium hexaboride, where the long-standing puzzle of the residual low-temperature conductivity has been shown to originate from robust surface states.

cond-mat.str-el↗

arXiv2015

Ultrafast observation of electron hybridization and in-gap states formation in Kondo insulator SmB6

SmB6 is a promising candidate for topological Kondo insulator. In this letter, we report ultrafast carrier dynamics of SmB6. Two characteristic temperatures: T1=100 K and T2= 20 K are observed. T1 corresponds to the opening of the f-d hybridization gap revealed by an abrupt disappearance of terahertz f-band plasmon oscillations. Between T1 and T2, a phonon bottleneck effect dominates the photocarrier relaxation processes. Below T2, we observe the formation of in-gap states, which are strongly affected by optically injected hot electrons and the transient electron temperature change.

cond-mat.str-el↗

arXiv2014

Evidence of Chiral Order in the Charge-Ordered Phase of Superconducting La1.875Ba0.125Cuo4 Single Crystals Using Polar Kerr-Effect Measurements

High resolution polar Kerr effect (PKE) measurements were performed on La1.875Ba0.125Cuo4 single crystals revealing that a finite Kerr signal is measured below an onset temperature-T_K that coincides with charge ordering transition temperature T_{CO}. We further show that the sign of the Kerr signal cannot be trained with magnetic field, is found to be the same of opposite sides of the same crystal, and is odd with respect to strain in the diagonal direction of the unit cell. These observations are consistent with a chiral "gyrotropic" order above T_c for La1.875Ba0.125Cuo4; similarities to other cuprates suggest that it is a universal property in the pseudogap regime.

cond-mat.str-el↗

arXiv2013

On a question of Babadi and Tarokh II

In this paper we continue to study a question proposed by Babadi and Tarokh \cite{ba2} on the mysterious randomness of Gold sequences. Upon improving their result, we establish the randomness of product of pseudorandom matrices formed from two linear block codes with respect to the empirical spectral distribution, if the dual distance of both codes is at least 5, hence providing an affirmative answer to the question.

cs.IT↗

arXiv2013

Weak Antilocalization and Linear Magnetoresistance in The Surface State of SmB6

Strongly correlated Kondo insulator SmB6 is known for its peculiar low temperature residual conduction, which has recently been demonstrated to arise from a robust metallic surface state, as predicted by the theory of topological Kondo insulator (TKI). Photoemission, quantum oscillation and magnetic doping experiments have provided evidence for the Dirac-like dispersion and topological protection. Questions arise as whether signatures of spin-momentum locking and electron interaction could be resolved in transport measurements. Here we report metallic conduction of surface state down to mK temperatures with saturation behaviors suggestive of Kondo effect. We observe in the surface state the weak-antilocalization (WAL) effect that is in agreement with a spin-momentum locked metallic surface. At larger perpendicular magnetic fields, the surface state exhibits an unusual linear magnetoresistance similar to those found in Bi-based topological insulators and in graphene. (Correspondence to: xia.jing@uci.edu)

cond-mat.str-el↗

arXiv2013

On a question of Babadi and Tarokh

In a recent remarkable paper, Babadi and Tarokh proved the "randomness" of sequences arising from binary linear block codes in the sense of spectral distribution, provided that their dual distances are sufficiently large. However, numerical experiments conducted by the authors revealed that Gold sequences which have dual distance 5 also satisfy such randomness property. Hence the interesting question was raised as to whether or not the stringent requirement of large dual distances can be relaxed in the theorem in order to explain the randomness of Gold sequences. This paper improves their result on several fronts and provides an affirmative answer to this question.

math.NT↗

arXiv2013

Robust Surface Hall Effect and Nonlocal Transport in SmB6: Indication for an Ideal Topological Insulator

A topological insulator (TI) is an unusual quantum state in which the insulating bulk is topologically distinct from vacuum, resulting in a unique metallic surface that is robust against time-reversal invariant perturbations. These surface transport properties, however, remains difficult to be isolated from the bulk in existing TI crystals (Bi2Se3, Bi2Te3 and Sb2Te3) due to impurity caused bulk conduction. We report in large crystals of topological Kondo insulator (TKI) candidate material SmB6 the thickness-independent surface Hall effects and non- local transport, which are robust against perturbations including mechanical abrasion. These results serve as proof that at low temperatures SmB6 has a robust metallic surface that surrounds a truly insulating bulk, paving the way for transport studies of the surface state in this proposed TKI material. (xia.jing@uci.edu).

cond-mat.str-el↗

arXiv2012

Evidence for a fractional quantum Hall state with anisotropic longitudinal transport

At high magnetic fields, where the Fermi level lies in the N=0 lowest Landau level (LL), a clean two-dimensional electron system (2DES) exhibits numerous incompressible liquid phases which display the fractional quantized Hall effect (FQHE) (Das Sarma and Pinczuk, 1997). These liquid phases do not break rotational symmetry, exhibiting resistivities which are isotropic in the plane. In contrast, at lower fields, when the Fermi level lies in the $N\ge2$ third and several higher LLs, the 2DES displays a distinctly different class of collective states. In particular, near half filling of these high LLs the 2DES exhibits a strongly anisotropic longitudinal resistance at low temperatures (Lilly et al., 1999; Du et al., 1999). These "stripe" phases, which do not exhibit the quantized Hall effect, resemble nematic liquid crystals, possessing broken rotational symmetry and orientational order (Koulakov et al., 1996; Fogler et al., 1996; Moessner and Chalker, 1996; Fradkin and Kivelson, 1999; Fradkin et al, 2010). Here we report a surprising new observation: An electronic configuration in the N=1 second LL whose resistivity tensor simultaneously displays a robust fractionally quantized Hall plateau and a strongly anisotropic longitudinal resistance resembling that of the stripe phases.

cond-mat.str-el↗