148 research outputs found

### Lattice electrons in constant magnetic field: Bethe like ansatz

We use the functional representation of Heisenberg-Weyl group and obtain
equation for the spectrum of the model, which is more complicated than Bethes
ones, but can be written explicitly through theta functions.Comment: 8 pages, LATE

### Zero-bias tunneling anomaly in a clean 2D electron gas caused by smooth density variations

We show that smooth variations, \delta n({\bf r}), of the local electron
concentration in a clean 2D electron gas give rise to a zero-bias anomaly in
the tunnel density of states, \nu(\omega), even in the absence of scatterers,
and thus, without the Friedel oscillations. The energy width, \omega_0, of the
anomaly scales with the magnitude, \delta n, and characteristic spatial extent,
D, of the fluctuations as (\delta n/D)^{2/3}, while the relative magnitude
\delta\nu/\nu scales as (\delta n/D). With increasing \omega, the averaged
\delta\nu oscillates with \omega. We demonstrate that the origin of the anomaly
is a weak curving of the classical electron trajectories due to the smooth
inhomogeneity of the gas. This curving suppresses the corrections to the
electron self-energy which come from the virtual processes involving two
electron-hole pairsComment: 4+ pages, 3 figure

### Smearing of the 2D Kohn anomaly in a nonquantizing magnetic field: Implications for the interaction effects

Thermodynamic and transport characteristics of a clean two-dimensional
interacting electron gas are shown to be sensitive to the weak perpendicular
magnetic field even at temperatures much higher than the cyclotron energy, when
the quantum oscillations are completely washed out. We demonstrate this
sensitivity for two interaction-related characteristics: electron lifetime and
the tunnel density of states. The origin of the sensitivity is traced to the
field-induced smearing of the Kohn anomaly; this smearing is the result of
curving of the semiclassical electron trajectories in magnetic field.Comment: 4.5 pages, 3 figures, published versio

### An Integrable Model with non-reducible three particle R-Matrix

We define an integrable lattice model which, in the notation of Yang, in
addition to the conventional 2-particle $R$-matrices also contains
non-reducible 3-particle $R$-matrices. The corresponding modified Yang-Baxter
equations are solved and an expression for the transfer matrix is found as a
normal ordered exponential of a (non-local) Hamiltonian.Comment: 13 pages, 4 figure

### The 3d Ising Model represented as Random Surfaces

We consider a random surface representation of the three-dimensional Ising
model.The model exhibit scaling behaviour and a new critical index \k which
relates \g_{string} for the bosonic string to the exponent \a of the
specific heat of the 3d Ising model is introduced. We try to determine \k by
numerical simulations.Comment: No figures included. Available by ordinary mail on request. 13 pages.
Latex. preprint NBI-HE-92-8

### Graphene valley polarization as a function of carrier-envelope phase in few-cycle laser pulses and its footprints in harmonic signals

We consider coherent dynamics of graphene charged carriers exposed to an
intense few-cycle linearly polarized laser pulse. The results, obtained by
solving the generalized semiconductor Bloch equations numerically in the
Hartree-Fock approximation, taking into account many-body Coulomb interaction,
demonstrate strong dependence of the valley polarization on the
carrier-envelope phase (CEP), which is interpolated by the simple sinusoidal
law. Then we consider harmonic generation in multi-cycle laser field by
graphene preliminary exposed to an intense few-cycle laser pulse. We show that
the second harmonic's intensity is a robust observable quantity that provides a
gauge of CEP for pulse durations up to two optical cycles, corresponding to 40
$\mathrm{fs}$ at the wavelength of 6.2 $\mathrm{\mu m}$.Comment: 9 pages, 10 figure

### Note on the thermodynamic Bethe Ansatz approach to the quantum phase diagram of the strong coupling ladder compounds

We investigate the low-temperature phase diagram of the exactly solved su(4)
two-leg spin ladder as a function of the rung coupling $J_{\perp}$ and magnetic
field $H$ by means of the thermodynamic Bethe Ansatz (TBA). In the absence of a
magnetic field the model exhibits three quantum phases, while in the presence
of a strong magnetic field there is no singlet ground state for ferromagnetic
rung coupling. For antiferromagnetic rung coupling, there is a gapped phase in
the regime H H_{c2} and a
Luttinger liquid magnetic phase in the regime H_{c1} < H < H_{c2}. The critical
behaviour derived using the TBA is consistent with the existing experimental,
numerical and perturbative results for the strong coupling ladder compounds.
This includes the spin excitation gap and the critical fields H_{c1} and
H_{c2}, which are in excellent agreement with the experimental values for the
known strong coupling ladder compounds (5IAP)_2CuBr_4 2H_2 O, Cu_2(C_5 H_{12}
N_2)_2 Cl_4 and (C_5 H_{12} N)_2 CuBr_4. In addition we predict the spin gap
$\Delta \approx J_{\perp}-{1/2}J_{\parallel}$ for the weak coupling compounds
with $J_{\perp} \sim J_{\parallel}$, such as (VO)_2 P_2 O_7, and also show that
the gap opens for arbitrary $J_{\perp}/ J_{\parallel}$.Comment: 10 pages, 3 figure

### Grassmann-Gaussian integrals and generalized star products

In quantum scattering on networks there is a non-linear composition rule for
on-shell scattering matrices which serves as a replacement for the
multiplicative rule of transfer matrices valid in other physical contexts. In
this article, we show how this composition rule is obtained using Berezin
integration theory with Grassmann variables.Comment: 14 pages, 2 figures. In memory of Al.B. Zamolodichiko

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