The work by T. K. Ghosh and K. Machida [ cond-mat/0510160 and Phys. Rev. A 73 , 013613 (2006)] on the sound velocity in a cylindrically confined Fermi superfluid obeying a power-law equation of state is shown to make use of an improper projection of the sound wave equation. This inaccuracy fully accounts for the difference between their results and those previously reported by Capuzzi et al. [ cond-mat/0509323 and Phys. Rev. A 73 , 021603(R) (2006)]. In this Comment we show that both approaches lead exactly to the same result when the correct weight function is used in the projection. Plots of the correct behavior of the phonon and monopole-mode spectra in the BCS, unitary, and BEC limits are also shown.
In a recent paper (cond-mat/0411197) we showed the equivalence of two seemingly contradictory theories on Griffiths-McCoy singularities (GMS) in metallic antiferromagnets close to a quantum critical point (QCP). In a recent comment, Millis {\it et al.} (cond-mat/0411738) argue that in heavy-fermion materials the electronic damping is large leading to the freezing of locally magnetically ordered droplets at high temperatures. In this reply we show that this erroneous conclusion is based on a treatment of the problem of disorder close to a QCP which is not self-consistent. We argue that a self-consistent treatment of the ordered droplets must lead to weak damping and to a large region of GMS behavior, in agreement with the our ealier results.
Recently, Phys. Rev. E 67, 051906 (2003)]] introduced the discrete persistent chain model which contains features both of the freely jointed chain (FJO) and the wormlike chain (WLC) models. Equation (20) of their paper is correct only in a special case of large l, the ratio of the persistence length to the monomer length. This special case is unnecessary because the general case can be studied just as easily. Working out the general case, we obtain the force extension relation correct for all values of the parameter l. This force extension relation reduces to the FJC result at small l and to the WLC at large l. At small force, it reduces to the result of Rosa et al. (e-print cond-mat/0307015).
Traditional discussions of the Second Law of Thermodynamics studied the limits of very specific types of devices, such as heat engines, chemical reactions, and molecules channeled by valves. Allahverdyan and Nieuwenhuizen (cond-mat/0110422) have come the closest to proving a more general form of the Second Law, applicable to field effect devices -- but recently (cond-mat/0408537) they have observed counterexamples and loopholes. This paper discusses recent field effect nanotechnologies which might permit a more substantial counterexample. Efforts were made to disprove the possibility of extracting electricity from ambient heat, from another perspective -- but these efforts led only to a new result on the equivalence of classical and quantum statistics, which may be important to the backwards-time interpretation of quantum mechanics.
In a recent Letter, Jiang, Sun, Xie and Wang [Phys. Rev. Lett. 93, 076802 (2004), cond-mat/0408261] study transport through an interacting quantum dot embedded in one arm of an Aharonov-Bohm interferometer. Based on a theoretical analysis of the Aharonov-Bohm oscillation amplitude, Jiang {\it et al.} claim, contrary to earlier work by two of us, that at finite temperature the intradot interaction will {\em not} lead to any dephasing. Likewise, they claim that the theoretically predicted and experimentally verified asymmetry of the Aharonov-Bohm oscillation amplitude is {\em not} associated with dephasing. In this Comment, we point out severe inconsistencies in the analysis of the Letter by Jian {\it et al.}, and show that their conclusions are ill-founded.
We have measured the c-axis angular-dependent magnetoresistance (AMR) of a Na0.48CoO2 single crystal, with a magnetic field of 10 T rotating within Co-O planes. Below the metal-insulator transition temperature at 40 K, the AMR is dominated by a twofold oscillation due to the charge ordering. The fourfold and sixfold oscillations in AMR become pronounced below 25 K. The presence of this fourfold oscillation is consistent with the picture proposed by Choy (cond-mat/0502164) that the Co lattice will split into two orthogonal sublattices with one occupied by Co3+ ions and the other by Co4+ ions in low temperatures. Embedded in these orthogonal sublattices, a hexagonal lattice, formed by Co4+ spins, leads to the sixfold oscillation in AMR.
This thesis gives an extension for the Density Matrix Renormalisation Group (DMRG) to two dimensions and described a newly developed combination of the DMRG and a Green Function Monte Carlo simulation (GFMC). The first two chapters focus on the DMRG method. The properties are reviewed and it is shown that good quality results can be obtained for two-dimensional systems through finite-size scaling. In the third and fourth chapter the properties of the two-dimensional frustrated Heisenberg model are analysed using a similar combination of DMRG and finite-size scaling. The final chapter presents the combination of the DMRG and GFMC with Stochastic Reconfiguration (Sorella, Capriotti cond-mat/9902211) We find an intermediate phase between Neel and collinear long-range order. This phase shows spatial inhomogeneities with a tendency towards plaquette formation.
In a recent preprint Campuzano et al.(cond-mat/0309402), have questioned the validity of our ARPES results (cond-mat/0305179) contradicting the interpretation of earlier photoemission experiments in terms of the time-reversal symmetry breaking in Bi2212. Here we highlight the principal results of our study and refute all the criticism.
Mohanty and Webb [Phys. Rev. Lett. 88, 146601 (2002), cond-mat/0204298] claim that their data on conductance fluctuations in gold wires contradict the one-parameter scaling. We show that flaws in extracting values of the cumulants (irreducible moments) > of the conductance distribution (for n=3,4) invalidate all the conclusions made there. The actual values of the cumulants determined by us from the published raw data contained in Ref. [Phys. Rev. Lett. 88, 146601 (2002)] are orders of magnitude smaller than those claimed. Moreover, the limited applicability of the ergodicity hypothesis makes the higher order cumulants extracted from magnetofingerprints statistically unreliable. Thus, the data of Ref. [Phys. Rev. Lett. 88, 146601 (2002)] do not warrant any statement on the violation or validity of the one-parameter scaling.
We study a one-dimensional model that undergoes a transition between an active and an absorbing phase. Monte Carlo simulations supported by some additional arguments prompted us to predict the exact location of the critical point and critical exponents in this model. The exponents delta=0.5 and z=2 follows from random-walk-type arguments. The exponents beta=nu( perpendicular) are found to be nonuniversal and encoded in the singular part of reactivation probability, as recently discussed by H. Hinrichsen (cond-mat/0008179). A related model with quenched randomness is also studied.
Comment on recent claims by Sornette and Zhou: D. Sornette and W. Zhou, Quantitative Finance 2 (6), 468-481 (2002); Evidence of a Worldwide Stock Market Log-Periodic Anti-Bubble Since Mid-2000, cond-mat/0212010; Renormalization Group Analysis of the 2000-2002 anti-bubble in the US SP 500 index, physics/0301023.
The recent claim by Kirkpatrick and Belitz (cond-mat/0111398) that Ward identities could be used to prove the absence of electron dephasing at T=0 contains serious flaws. These authors try to draw conclusions about dephasing from an analysis of the diffuson, which is not sensitive to this process. The Cooperon, which does contain this information, is analyzed only in time reversal symmetric situations, which by assumption excludes any relaxation and dephasing. Hence, their analysis remains inconclusive for the problem in question.
Recently, Aji and Goldenfeldt [Phys. Rev. Lett. 87, 197003 (2001), cond-mat/0105622] put forward an explanation for the value of the dynamic critical exponent z observed in certain Monte Carlo simulations of the superconducting phase transition in zero magnetic field. In this Comment, we point out that their analysis is based on incorrect assumptions regarding the scaling dimension of the vortex density.