202 research outputs found
Spectral functions of strongly interacting isospin-1/2 bosons in one dimension
We study a system of one-dimensional (iso)spin-1/2 bosons in the regime of
strong repulsive interactions. We argue that the low-energy spectrum of the
system consists of acoustic density waves and the spin excitations described by
an effective ferromagnetic spin chain with a small exchange constant J. We use
this description to compute the dynamic spin structure factor and the spectral
functions of the system.Comment: reference adde
Asymmetric Zero-Bias Anomaly for Strongly Interacting Electrons in One Dimension
We study a system of one-dimensional electrons in the regime of strong
repulsive interactions, where the spin exchange coupling J is small compared
with the Fermi energy, and the conventional Tomonaga-Luttinger theory does not
apply. We show that the tunneling density of states has a form of an asymmetric
peak centered near the Fermi level. In the spin-incoherent regime, where the
temperature is large compared to J, the density of states falls off as a power
law of energy \epsilon measured from the Fermi level, with the prefactor at
positive energies being twice as large as that at the negative ones. In
contrast, at temperatures below J the density of states forms a split peak with
most of the weight shifted to negative \epsilon.Comment: 4 pages, 2 figure
Resonant Josephson current through a quantum dot
We calculate the DC Josephson current through a semiconducting quantum dot
which is weakly coupled by tunnel barriers to two superconducting reservoirs. A
Breit-Wigner resonance in the conductance corresponds to a resonance in the
critical current, but with a different (non-lorentzian) lineshape.Comment: 5 pages including 1 figure; this paper was published in the
proceedings of SQUID'91; it is archived here because of its relevance to
cond-mat/011148
Renormalization of impurity scattering in one-dimensional interacting electron systems in magnetic field
We study the renormalization of a single impurity potential in
one-dimensional interacting electron systems in the presence of magnetic field.
Using the bosonization technique and Bethe ansatz solutions, we determine the
renormalization group flow diagram for the amplitudes of scattering of up- and
down-spin electrons by the impurity in a quantum wire at low electron density
and in the Hubbard model at less than half filling. In the absence of magnetic
field the repulsive interactions are known to enhance backscattering and make
the impurity potential impenetrable in the low-energy limit. On the contrary,
we show that in a strong magnetic field the interaction may suppress the
backscattering of majority-spin electrons by the impurity potential in the
vicinity of the weak-potential fixed point. This implies that in a certain
temperature range the impurity becomes almost transparent for the majority-spin
electrons while it is impenetrable for the minority-spin ones. The impurity
potential can thus have a strong spin-filtering effect.Comment: 11 pages, 2 figures; v2: a typo corrected and a reference added; v3:
published version, Sec.II revised with an additional explanatory subsection,
comments on the case of more than half-filling added, typos corrected, a
reference update
Low Energy Properties of the Random Spin-1/2 Ferromagnetic-Antiferromagnetic Heisenberg Chain
The low energy properties of the spin-1/2 random Heisenberg chain with
ferromagnetic and antiferromagnetic interactions are studied by means of the
density matrix renormalization group (DMRG) and real space renormalization
group (RSRG) method for finite chains. The results of the two methods are
consistent with each other. The deviation of the gap distribution from that of
the random singlet phase and the formation of the large-spin state is observed
even for relatively small systems. For a small fraction of the ferromagnetic
bond, the effect of the crossover to the random singlet phase on the low
temperature susceptibility and specific heat is discussed. The crossover
concentration of the ferromagnetic bond is estimated from the numerical data.Comment: 11 pages, revtex, figures upon reques
Density Matrix Renormalization Group Method for the Random Quantum One-Dimensional Systems - Application to the Random Spin-1/2 Antiferromagnetic Heisenberg Chain -
The density matrix renormalization group method is generalized to one
dimensional random systems. Using this method, the energy gap distribution of
the spin-1/2 random antiferromagnetic Heisenberg chain is calculated. The
results are consistent with the predictions of the renormalization group theory
demonstrating the effectiveness of the present method in random systems. The
possible application of the present method to other random systems is
discussed.Comment: 13 pages, 3 figures upon reques
Aperiodic quantum XXZ chains: Renormalization-group results
We report a comprehensive investigation of the low-energy properties of
antiferromagnetic quantum XXZ spin chains with aperiodic couplings. We use an
adaptation of the Ma-Dasgupta-Hu renormalization-group method to obtain
analytical and numerical results for the low-temperature thermodynamics and the
ground-state correlations of chains with couplings following several two-letter
aperiodic sequences, including the quasiperiodic Fibonacci and other
precious-mean sequences, as well as sequences inducing strong geometrical
fluctuations. For a given aperiodic sequence, we argue that in the easy-plane
anisotropy regime, intermediate between the XX and Heisenberg limits, the
general scaling form of the thermodynamic properties is essentially given by
the exactly-known XX behavior, providing a classification of the effects of
aperiodicity on XXZ chains. We also discuss the nature of the ground-state
structures, and their comparison with the random-singlet phase, characteristic
of random-bond chains.Comment: Minor corrections; published versio
Kondo Problems in Tomonaga-Luttinger liquids
Quantum impurity problems in Tomonaga-Luttinger liquids (TLLs) are reviewed
with emphasis on their analogy to the Kondo problem in Fermi liquids. First,
the problem of a static impurity in a spinless TLL is considered, which is
related to the model studied in the context of the macroscopic quantum
coherence. In the low-energy limit the TLL is essentially cut into two pieces
when interaction is repulsive. The orthogonality catastrophe in a TLL is then
discussed. Finally, the Kondo effect of a spin-1/2 impurity in a
one-dimensional repulsively interacting electron liquids (a spinful TLL) is
reviewed. Regardless of the sign of the exchange coupling, the impury spin is
completely screened in the ground state. The leading low-temperature
contributions to thermodynamic quantities come from boundary contributions of a
bulk leading irrelevant operator.Comment: 7 pages, submitted to a special edition of JPSJ "Kondo Effect -- 40
Years after the Discovery"; corrected typos, added reference
The Low-Energy Fixed Points of Random Quantum Spin Chains
The one-dimensional isotropic quantum Heisenberg spin systems with random
couplings and random spin sizes are investigated using a real-space
renormalization group scheme. It is demonstrated that these systems belong to a
universality class of disordered spin systems, characterized by weakly coupled
large effective spins. In this large-spin phase the uniform magnetic
susceptibility diverges as 1/T with a non-universal Curie constant at low
temperatures T, while the specific heat vanishes as T^delta |ln T| for T->0.
For broad range of initial distributions of couplings and spin sizes the
distribution functions approach a single fixed-point form, where delta \approx
0.44. For some singular initial distributions, however, fixed-point
distributions have non-universal values of delta, suggesting that there is a
line of fixed points.Comment: 19 pages, REVTeX, 13 figure
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