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Shou-Cheng Zhang

Publications and source records attributed to Shou-Cheng Zhang.

At least 199 records · Page 11Linked to original sources
arXiv2003

Dissipationless Quantum Spin Current at Room Temperature

While microscopic laws of physics are invariant under the reversal of the arrow of time, the transport of energy and information in most devices is an irreversible process. It is this irreversibility that leads to intrinsic dissipations in electronic devices and limits the possibility of quantum computation. We theoreticallypredict that the electric field can induce a substantial amount of dissipationless quantum spin current at room temperature, in hole doped semiconductors such as Si, Ge and GaAs. Based on a generalization of the quantum Hall effect, the predicted effect leads to efficient spin injection without the need for metallic ferromagnets. Principles found in this work could enable quantum spintronic devices with integrated information processing and storage units, operating with low power consumption and performing reversible quantum computation.

cond-mat.mes-hall↗
arXiv2002

Exact microscopic wave function for a topological quantum membrane

The higher dimensional quantum Hall liquid constructed recently supports stable topological membrane excitations. Here we introduce a microscopic interacting Hamiltonian and present its exact ground state wave function. We show that this microscopic ground state wave function describes a topological quantum membrane. We also construct variational wave functions for excited states using the non-commutative algebra on the four sphere. Our approach introduces a non-perturbative method to quantize topological membranes.

cond-mat.mes-hall↗
arXiv2002

To see a world in a grain of sand

Throughout John Wheeler's career, he wrestled with big issues like the fundamental length, the black hole and the unification of quantum mechanics and relativity. In this essay, I argue that solid state physics -- historically the study of silicon, semiconductors and sand grains -- can give surprisingly deep insights into the big questions of the world.

hep-th↗
arXiv2002

Effective field theory description of the higher dimensional quantum Hall liquid

We derive an effective topological field theory model of the four dimensional quantum Hall liquid state recently constructed by Zhang and Hu. Using a generalization of the flux attachment transformation, the effective field theory can be formulated as a U(1) Chern-Simons theory over the total configuration space $CP_3$, or as a SU(2) Chern-Simons theory over $S^4$. The new quantum Hall liquid supports various types of topological excitations, including the 0-brane (particles), the 2-brane (membranes) and the 4-brane. There is a topological phase interaction among the membranes which generalizes the concept of fractional statistics.

cond-mat↗
arXiv2002

Tuning order in cuprate superconductors

This article presents our perspective on STM measurements by Hoffman et al. (cond-mat/0201348) of the vortex lattice in BSCCO. We discuss implications of these measurements for various theories of the cuprate superconductors.

cond-mat.supr-con↗
arXiv2001

Collective excitations at the boundary of a 4D quantum Hall droplet

In this work we investigate collective excitations at the boundary of a recently constructed 4D quantum Hall state. Local bosonic operators for creating these collective excitations can be constructed explicitly. Massless relativistic wave equations with helicity $S$ can be derived exactly for these operators from their Heisenberg equation of motion. For the S=1 and S=2 cases these equations reduce to the free Maxwell and linearized Einstein equation respectively. These collective excitations can be interpreted as hydrodynamical modes at the boundary of the 4D QHE droplet. Outstanding issues are critically discussed.

cond-mat.mes-hall↗
arXiv2001

Theory of Static and Dynamic Antiferromagnetic Vortices in LSCO Superconductors

A key prediction of the SO(5) theory is the antiferromagnetic vortex state. Recent neutron scattering experiment on LSCO superconductors revealed enhanced antiferromagnetic order in the vortex state. Here we review theoretical progress since the original proposal and present a theory of static and dynamic antiferromanetic vortices in LSCO superconductors. It is shown that the antiferromagnetic region induced by the vortices can be greater than the coherence length, due to the light effective mass of the dynamic antiferromagnetic fluctuations at optimal doping, and close promixity to the antiferromagentic state in the underdoped regime. Systematic experiments are proposed to unambiguously determine that the field induced magnetic scattering originates from the vortices and not from the bulk.

cond-mat.supr-con↗
arXiv2001

A Four Dimensional Generalization of the Quantum Hall Effect

We construct a generalization of the quantum Hall effect, where particles move in four dimensional space under a SU(2) gauge field. This system has a macroscopic number of degenerate single particle states. At appropriate integer or fractional filling fractions the system forms an incompressible quantum liquid. Gapped elementary excitations in the bulk interior and gapless elementary excitations at the boundary are investigated.

cond-mat↗
arXiv2001

Dispersoin of the πresonance

We study the dispersion of the $π$ resonance in the superconducting state within the projected SO(5) model\cite{project}. Away from the the commensurate momentum, the propagation of the $π$ resonance creates phase slips in the superconducting order parameter. This frustration effect leads to a strong dressing of the $π$ resonance and a downwards dispersion away from the commensurate wave vector. Based on these results, we argue that the the commensurate resonance and incommensurate magnetic fluctuations in the cuprates are continuously connected.

cond-mat.supr-con↗
arXiv2000

Current Induced Magnetization Switching in Small Domains of Different Anisotropies

Several recent experimental studies have confirmed the possibility of switching the magnetization direction in the small magnetic domains by pumping large spin-polarized currents through them. On the basis of equations proposed by J.Slonczewski for the case when magnetization of the domains is almost uniform, we analyze the stability and switching for two types of magnetic and shape anisotropies of a magnetic domain in a nanowire and find qualitatively different behavior, including different shapes of bistable regions. Our study is analytic as opposed to recent numeric work. Assumed anisotropies can be realized in experiments and our predictions can be used to experimentally test the theory of spin-transfer torques. Such test would be especially interesting since alternative approaches are discussed in the literature.

cond-mat↗
arXiv2000

Interrelation of Superconducting and Antiferromagnetic Gaps in High-Tc Compounds: a Test Case for the SO(5) Theory

Recent angle resolved photoemission data, which found evidence for a d-wave-like modulation of the antiferromagnetic gap, suggest an intimate interrelation between the antiferromagnetic insulator and the superconductor with its d-wave gap. It is shown here that a projected SO(5) theory, which explicitly takes the Mott-Hubbard gap into account, correctly describes the observed gap characteristics. Specifically, it accounts for the order of magnitude difference between the antiferromagnetic gap modulation and the superconducting gap and is also consistent with the gap dispersion.

cond-mat.str-el↗
arXiv2000

How to experimentally measure the number 5 of the SO(5) theory?

According to Wilson's theory of critical phenomena, critical exponents are universal functions of $d$, the dimension of space, and $n$, the dimension of the symmetry group. SO(5) theory of antiferromagnetism and superconductivity predicts a bicritical point where $T_N$ and $T_c$ intersect. By measuring critical exponents close to the bicritical point, and knowing that $d=3$, one can experimentally measure the number 5 of the SO(5) theory.

cond-mat.supr-con↗
arXiv1999

SO(5) Superconductors in a Zeeman Magnetic Field

The generic symmetry of a system under a uniform Zeeman magnetic field is U(1) x U(1). However, we show that SO(5) models in the presence of a finite chemical potential and a finite Zeeman magnetic field can have a exact SU(2) x U(1) symmetry. This principle can be used to test SO(5) symmetry at any doping level.

cond-mat.supr-con↗
arXiv1999

Projected SO(5) Models

We construct a class of projected SO(5) models where the Gutzwiller constraint of no-double-occupancy is implemented exactly. We introduce the concept of projected SO(5) symmetry where all static correlation functions are exactly SO(5) symmetric and discuss the signature of the projected SO(5) symmetry in dynamical correlation functions. We show that this class of projected SO(5) models can give a realistic description of the global phase diagram of the high T_c superconductors and account for many of their physical properties.

cond-mat↗
arXiv1999

Interrelation of Superconducting and Antiferromagnetic Gaps in High-Tc Compounds: a Test Case for a Microscopic Theory

Recent angle resolved photoemission (ARPES) data, which found evidence for a d-wave-like modulation of the antiferromagnetic gap, suggest an intimate interrelation between the antiferromagnetic insulator and the superconductor with its d-wave gap. This poses a new challenge to microscopic descriptions, which should account for this correlation between, at first sight, very different states of matter. Here, we propose a microscopic mechanism which provides a definite correlation between these two different gap structures: it is shown that a projected SO(5) theory, which aims at unifying antiferromagnetism and d-wave superconductivity via a common symmetry principle while explicitly taking the Mott-Hubbard gap into account, correctly describes the observed gap characteristics. Specifically, it accounts for both the dispersion and the order of magnitude difference between the antiferromagnetic gap modulation and the superconducting gap.

cond-mat.str-el↗
arXiv1999

Resonant neutron scattering on the high Tc cuprates and pi and eta excitation of the t-J and Hubbard models

We review the explanation for resonant neutron scattering experiments in $YBa_2Cu_3O_{6+δ}$ and $Bi_2 Sr_2 Ca_2 O_{8+δ}$ materials from the point of view of triplet excitation in the particle-particle channel, the pi excitation. Relation of these resonances to the superconducting condensation energy and their role in stabilizing the superconducting state is discussed. Due to the superconducting fluctuations, the pi resonance may appear as a broad peak above Tc. Analogue problem to the pi excitation for the case of s-wave pairing, the eta excitation, is considered in the strong coupling limit with an emphasis on the resonance precursors in a state with no long range order.

cond-mat.str-el↗
arXiv1999

Quantitative Determination of a Microscopic Mechanism of High Tc Superconductivity

Within the t-J model of copper-oxides, the condensation energy can be related to the change in the dynamical spin structure factor between the superconducting and the normal states. By analyzing previous experimental data, we show that the change associated with the resonant neutron scattering peak found in $YBa_2Cu_3O_7$ can quantitatively account for the condensation energy. We argue that this analysis suggests a microscopic mechanism for high Tc superconductivity.

cond-mat.str-el↗