Perovskite solar cells (PSC), with their high efficiency, low production costs, and diverse uses, have emerged as a viable technology for sustainable energy generation. The present study examines perovskite solar cells' benefic aspects and associated constraints, emphasizing their potential for futuristic advancement. Furthermore, the remarkable applications of perovskites in energy generation encouraged us to investigate the Power conversion efficiency (PCE) of perovskite solar cells compared with other solar energy technologies. Lastly, to resolve issues and promote their equitable adoption, the study presented recommendations for subsequent investigation and advancement.
The conclusions of a recent paper by Olsson (Phys. Rev. Lett. 75, 2758 (1995), cond-mat/9506082) about the fully frustrated XY model in two dimensions are questioned. In particular, the evidence presented for having two separate chiral and U(1) phase transitions are critically considered.
In a recent paper, Phys. Rev. Lett. 81, 1074 (1998), Golubev and Zaikin (GZ) found that ``zero-point fluctuations of electrons'' contribute to the dephasing rate extracted from the magnetoresistance. As a result, the dephasing rate remains finite at zero temperature. GZ claimed that their results ``agree well with the experimental data''. We point out that the GZ results are incompatible with (i) conventional perturbation theory of the effects of interaction on weak localization (WL), and (ii) with the available experimental data. More detailed criticism of GZ findings can be found in cond-mat/9808053.
Abstract The Hamiltonian Mean Field (HMF) model describes a system of N fully coupled particles showing a second-order phase transition as a function of the energy. The dynamics of the model presents interesting features in a small energy region below the critical point. In particular, when the particles are prepared in a “water bag” initial state, the relaxation to equilibrium is very slow. In the transient time the system lives in a dynamical quasi-stationary state and exhibits anomalous (enhanced) diffusion and Levy walks. In this paper we study temperature and velocity distribution of the quasi-stationary state and we show that the lifetime of such a state increases with N . In particular when the N →∞ limit is taken before the t →∞ limit, the results obtained are different from the expected canonical predictions. This scenario seems to confirm a recent conjecture proposed by Tsallis [C. Tsallis, in: S.R.A. Salinas, C. Tsallis (Eds.), Nonextensive statistical mechanics and thermodynamics, Braz. J. Phys. 29 (1999) 1 cond-mat/9903356 and contribution to this conference.
Abstract We present a Fermi liquid model for the overdoped and optimally doped cuprate superconductors. For the normal state, we provide an analytic demonstration, backed by self-consistent Baym–Kadanoff (BK) numerical calculations, of the linear in temperature resistivity and linear in 1/energy optical conductivity, provided the interacting Fermi liquid has strong peaks in its density of states (van-Hove singularities in two dimensions) near the chemical potential μ . Recent ARPES experiments by Valla et al. (Science 285 (1999) 2110, and preprint cond-mat/0003407) directly support the linearity of the one-particle scattering rate everywhere in the Brillouin zone hereto obtained. We show that the origin of this linearity is the linear in energy term of the imaginary part of the carrier susceptibility. Moreover, we verify that the interactions tend to pin the van-Hove singularities close to μ . We show that the low energy dependence of the susceptibility can have a purely fermionic origin. We introduce an ansatz for the susceptibility of the carriers, which we postulate to be enhanced in an additive manner due to the weak antiferromagnetic order of the CuO 2 planes. Inter alia, this ansatz may explain the appearance of the spin resonance peak (observed in neutron scattering) in the normal state of the cuprates. Further, we obtain particularly high transition temperatures T c from our BK–Eliashberg scheme by using this ansatz: we have a d x 2 − y 2 gap with T c >120 K for nearest neighbour hopping t =250 meV.
In cond-mat/9907125 the low-temperature behavior of a model for RNA secondary structure was studied. It is claimed that the model exhibits a breaking of the replica symmetry, since the width of the distribution P(q) of overlaps may converge to a finite value at T=0. The authors used an exact enumeration method to obtain all ground states for a given RNA sequence. Because of the exponential growing degeneracy, only sequences up to length L=256 could be studied. Here it is shown that, in contrast to the previous results, by going to much larger sizes as L=2000 the variance coverges towards zero, i.e. P(q) is a delta-function in the thermodynamic limit.
A. Chubukov, P. Monthoux, Dirk K. Morr University of Wisconsin-Madison
et al.
We argue that recent calculations by Amin and Stamp (PRL 77, 301 (1996); cond-mat/9601086) overestimate the strength of the vertex corrections in the spin-fermion model for cuprates. We clarify the physical origin of the apparent discrepancy between their results and earlier calculations. We also comment on the relative sign of the vertex correction.
Using explicit results for the four-point correlation functions of the Wess–Zumino–Novikov–Witten (WZNW) model we discuss the conformal embedding osp(4|4)1 = osp(2|2)−2 ⊕ su(2)0. This embedding has emerged in Bernard and LeClair's recent paper cond-mat/003075. Given that the osp(4|4)1 WZNW model is a free theory with power law correlation functions, whereas the su(2)0 and osp(2|2)−2 models are CFTs with logarithmic correlation functions, one immediately wonders whether or not it is possible to combine these logarithms and obtain simple power laws. Indeed, this very concern has been raised in a revised version of cond-mat/003075. In this paper we demonstrate how one may recover the free field behaviour from a braiding of the solutions of the su(2)0 and osp(2|2)−2 Knizhnik–Zamolodchikov equations. We do this by implementing a procedure analogous to the conformal bootstrap programme Nucl. Phys. B 241 (1984) 333. Our ability to recover such simple behaviour relies on a remarkable identity in the theory of elliptic integrals known as Legendre's relation.
In a recent Letter Simon and Lee suggested a scaling law for thermodynamic and kinetic properties of superconductors with lines of gap nodes. However their crossover parameter between the bulk dominated regime and the vortex dominated regime is different from that found in our paper (N.B. Kopnin and G.E. Volovik, JETP Lett., {\bf 64}, 690 (1996); see also cond-mat/9702093). We discuss the origin of the disagreement.
We study the energy distribution function of quasiparticles in short voltage biased mesoscopic wires in the presence of magnetic impurities and applied magnetic field. The system is described by a Boltzmann equation where the collision integral is determined by coupling to spin-$\frac{1}{2}$ impurities. We develop a theory of the coupling of nonequilibrium electrons to dissipative spins. This theory is valid as long as the characteristic smearing of the steps in the energy distribution function, which depends both on the bias voltage and the location of the probe, exceeds the Kondo temperature. We further address the renormalization of coupling constants by nonequilibrium electrons. Magnetic-field dependence of the energy relaxation rate turns out to be nonmonotonic. For low magnetic field an enhancement of energy relaxation is found, whereas for larger magnetic fields the energy relaxation decreases again meeting qualitatively the experimental findings by Anthore et al. (cond-mat/0109297). This gives a strong indication that magnetic impurities are in fact responsible for the enhanced energy relaxation in copper wires. Our theoretical results are in good agreement with the experiment at large bias voltages where the theory is applicable. At the same time, at small bias voltages there are substantial quantitative deviations. Furthermore, the concentration of the spins, which follows from the energy relaxation for Cu, seems to to be substantially higher than the concentration estimated from weak localization (dephasing rate) measurements. Since the approach presented is valid only above Kondo temperature, it does not apply to the related problem of weak localization at low temperature in equilibrium.
In a recent communication to the cond-mat archives, Suslov [cond-mat/0105325] severely criticizes a multitude of numerical results obtained by various groups for the critical exponent $\nu$ of the localization length at the disorder-induced metal-insulator transition in the three-dimensional Anderson model of localization as ``entirely absurd'' and ``evident desinformation''. These claims are based on the observation that there still is a large disagreement between analytical, numerical and experimental results for the critical exponent. The author proposes, based on a ``simple procedure to deal with corrections to scaling'', that the numerical data support nu approx 1, whereas recent numerical papers find nu = 1.58 +/- 0.06. As we show here, these claims are entirely wrong. The proposed scheme does neither yield any improved accuracy when compared to the existing finite-size scaling methods, nor does it give nu approx 1 when applied to high-precision data. Rather, high-precision numerics with error epsilon approx 0.1% together with all available finite-size-scaling methods evidently produce a critical exponent nu approx 1.58.
The Kondo effect in superconductors is frequently investigated using the local quasiparticle density of states as sole bath characteristics, i.e., the presence of anomalous propagators is ignored. Here we point out that this treatment is exact for a number of situations, including point-like impurities in d-wave superconductors. We comment on recent investigations [M. Matsumoto and M. Koga, J. Phys. Soc. Jpn. 70, 2860 (2001), cond-mat/0011256, and Phys. Rev. B 65, 024508 (2002), cond-mat/0103053] which reached different conclusions: while their numerical results are likely correct, their interpretation in terms of two-channel Kondo physics and an "orbital effect of Cooper pairs" is incorrect.
Recently, Hermele et al. claimed that the infrared (IR) fixed point of noncompact QED{sub 3} is stable against instanton excitations in the limit of large flavors of massless Dirac fermions [M. Hermele et al., cond-mat/0404751, Phys. Rev. B (to be published October 2004)]. We investigate an effect of nonmagnetic disorder on the deconfined quantum critical phase dubbed U(1) spin liquid (U1SL) in the context of quantum antiferromagnet. In the case of weak disorder the IR fixed point remains stable against the presence of both the instanton excitations and nonmagnetic disorder and thus the U1SL is sustained. In the case of strong disorder the IR fixed point becomes unstable against the disorder and the Anderson localization is expected to occur. We argue that in this case deconfinement of spinons does not occur since the Dirac fermion becomes massive owing to the localization.