Biomedical subjects

Junren Shi

Publications and source records attributed to Junren Shi.

9 recordsLinked to original sources

PubMed2006

Proper definition of spin current in spin-orbit coupled systems.

The conventional definition of spin current is incomplete and unphysical in describing spin transport in systems with spin-orbit coupling. A proper and measurable spin current is established in this study, which fits well into the standard framework of near-equilibrium transport theory and has the desirable property to vanish in insulators with localized orbitals. Experimental implications of our theory are discussed.

Journal Article↗

PubMed2005

Berry phase correction to electron density of states in solids.

Liouville's theorem on the conservation of phase-space volume is violated by Berry phase in the semiclassical dynamics of Bloch electrons. This leads to a modification of the phase-space density of states, whose significance is discussed in a number of examples: field modification of the Fermi-sea volume, connection to the anomalous Hall effect, and a general formula for orbital magnetization. The effective quantum mechanics of Bloch electrons is also sketched, where the modified density of states plays an essential role.

Journal Article↗

PubMed2005

Multiple bosonic mode coupling in the electron self-energy of (La2-xSrx)CuO4.

High resolution angle-resolved photoemission spectroscopy data along the (0,0)-(pi,pi) nodal direction with significantly improved statistics reveal fine structure in the electron self-energy of the underdoped (La2-xSrx)CuO4 samples in the normal state. Fine structure at energies of (40-46) meV and (58-63) meV, and possible fine structure at energies of (23-29) meV and (75-85) meV, have been identified. These observations indicate that, in (La2-xSrx)CuO4, more than one bosonic modes are involved in the coupling with electrons.

Journal Article↗

PubMed2005

Low temperature disordered phase of alpha-Pb/Ge(111).

A new structural phase transition has been observed at low temperature for the one-third of a monolayer (alpha phase) of Pb on Ge(111) using a variable-temperature scanning tunneling microscope. The well-known (sqrt[3] x sqrt[3])R30 degrees to (3 x 3) transition is accompanied by a new structural phase transition from (3 x 3) to a disordered phase at approximately 76 K. The formation of this "glasslike" phase is a consequence of competing interactions on different length scales.

Journal Article↗

PubMed2004

Ferromagnetic stability in Fe nanodot assemblies on Cu(111) induced by indirect coupling through the substrate.

We report collective ferromagnetic behavior with high Curie temperatures (T(c)) in Fe dot assemblies supported by the Cu(111) surface. Our ability to tune the average size and spacing of the individual dots allows us to conclude that enhanced magnetic anisotropy cannot account for this high-T(c) ferromagnetic order. Because our Monte Carlo simulations have ruled out the dipolar interaction as the dominant factor in this system, we attribute the origin of the ferromagnetic order to indirect exchange coupling via the Cu(111) substrate.

Journal Article↗

PubMed2004

Direct extraction of the Eliashberg function for electron-phonon coupling: a case study of Be(10(-)10).

We propose a systematic procedure to directly extract the Eliashberg function for electron-phonon coupling from high-resolution angle-resolved photoemission measurement. The procedure is successfully applied to the Be(10(-)10) surface, providing new insights into electron-phonon coupling at this surface. The method is shown to be robust against imperfections in experimental data and suitable for wider applications.

Journal Article↗

PubMed2003

Radiation-induced "zero-resistance state" and the photon-assisted transport.

We demonstrate that the radiation-induced "zero-resistance state" observed in a two-dimensional electron gas is a result of the nontrivial structure of the density of states of the systems and the photon-assisted transport. A toy model of a quantum tunneling junction with oscillatory density of states in leads catches most of the important features of the experiments. We present a generalized Kubo-Greenwood conductivity formula for the photon-assisted transport in a general system and show essentially the same nature of the transport anomaly in a uniform system.

Journal Article↗

PubMed2003

Surface phase transitions induced by electron mediated adatom-adatom interaction.

We propose that the indirect adatom-adatom interaction mediated by the conduction electrons of a metallic surface is responsible for the sqrt[3]xsqrt[3]<==>3x3 structural phase transitions observed in Sn/Ge (111) and Pb/Ge (111). When the indirect interaction overwhelms the local stress field imposed by the substrate registry, the system suffers a phonon instability, resulting in a structural phase transition in the adlayer. Our theory is capable of explaining all the salient features of the sqrt[3]xsqrt[3]<==>3x3 transitions observed in Sn/Ge (111) and Pb/Ge (111), and is in principle applicable to a wide class of systems whose surfaces are metallic before the transition.

Journal Article↗

PubMed2002

Droplet state and the compressibility anomaly in dilute 2D electron systems.

We investigate the space distribution of carrier density and the compressibility of two-dimensional (2D) electron systems by using the local density approximation. The strong correlation is simulated by the local exchange and correlation energies. A slowly varied disorder potential is applied to simulate the disorder effect. We show that the compressibility anomaly observed in 2D systems which accompanies the metal-insulator transition can be attributed to the formation of the droplet state due to a disorder effect at low carrier densities.

Journal Article↗