Electron Transport in Granular Metals

We consider thermodynamic and transport properties of a long granular array with strongly connected grains (inter-grain conductance g>>1.) We find that the system exhibits activated behavior of conductance and thermodynamic density of states ~exp(-T*/T) where the gap, T*, is parametrically larger than the energy at which conventional perturbation theory breaks down. The scale T* represents energy needed to create a long single-electron charge soliton propagating through the array.Comment: 4 pages, 1 figur

Coulomb Blockade with Dispersive Interfaces

What quantity controls the Coulomb blockade oscillations if the dot--lead conductance is essentially frequency--dependent ? We argue that it is the ac dissipative conductance at the frequency given by the effective charging energy. The latter may be very different from the bare charging energy due to the interface--induced capacitance (or inductance). These observations are supported by a number of examples, considered from the weak and strong coupling (perturbation theory vs. instanton calculus) perspectives.Comment: 4 page

Layered XY-Models, Anyon Superconductors, and Spin-Liquids

The partition function of the double-layer $XY$ model in the (dual) Villain form is computed exactly in the limit of weak coupling between layers. Both layers are found to be locked together through the Berezinskii-Kosterlitz-Thouless transition, while they become decoupled well inside the normal phase. These results are recovered in the general case of a finite number of such layers. When re-interpreted in terms of the dual problems of lattice anyon superconductivity and of spin-liquids, they also indicate that the essential nature of the transition into the normal state found in two dimensions persists in the case of a finite number of weakly coupled layers.Comment: 10 pgs, TeX, LA-UR-94-394

Fractional-flux vortices and spin superfluidity in triplet superconductors

We discuss a novel type of fractional flux vortices along with integer flux vortices in Kosterlitz-Thouless transitions in a triplet superconductor. We show that under certain conditions a spin-triplet superconductor should exhibit a novel state of {\it spin superfluidity} without superconductivity.Comment: Physical Review Lettes, in print. v2: references added, v3: discussion of several points extended according to referee request. Latest updates and links to related papers are available at my homepage http://people.ccmr.cornell.edu/~egor

Two-instanton approximation to the Coulomb blockade problem

We develop the two-instanton approximation to the current-voltage characteristic of a single electron transistor within the Ambegaokar-Eckern-Sch\"on model. We determine the temperature and gate voltage dependence of the Coulomb blockade oscillations of the conductance and the effective charge. We find that a small (in comparison with the charging energy) bias voltage leads to significant suppression of the Coulomb blockade oscillations and to appearance of the bias-dependent phase shift

Charge relaxation resistance in the Coulomb blockade problem

We study the dissipation in a system consisting of a small metallic island coupled to a gate electrode and to a massive reservoir via single tunneling junction. The dissipation of energy is caused by a slowly oscillating gate voltage. We compute it in the regimes of weak and strong Coulomb blockade. We focus on the regime of not very low temperatures when electron coherence can be neglected but quantum fluctuations of charge are strong due to Coulomb interaction. The answers assume a particularly transparent form while expressed in terms of specially chosen physical observables. We discovered that the dissipation rate is given by a universal expression in both limiting cases.Comment: 21 pages, 12 figure

Optimal fluctuation approach to a directed polymer in a random medium

A modification of the optimal fluctuation approach is applied to study the tails of the free energy distribution function P(F) for an elastic string in quenched disorder both in the regions of the universal behavior of P(F) and in the regions of large fluctuations, where the behavior of P(F) is non-universal. The difference between the two regimes is shown to consist in whether it is necessary or not to take into account the renormalization of parameters by the fluctuations of disorder in the vicinity of the optimal fluctuation.Comment: 4 pages, no figure

Nonperturbative interaction effects in the thermodynamics of disordered wires

We study nonperturbative interaction corrections to the thermodynamic quantities of multichannel disordered wires in the presence of the Coulomb interactions. Within the replica nonlinear $\sigma$-model (NL$\sigma$M) formalism, they arise from nonperturbative soliton saddle points of the NL$\sigma$M action. The problem is reduced to evaluating the partition function of a replicated classical one dimensional Coulomb gas. The state of the latter depends on two parameters: the number of transverse channels in the wire, N_{ch}, and the dimensionless conductance, G(L_T), of a wire segment of length equal to the thermal diffusion length, L_T. At relatively high temperatures, $G(L_T) \gtrsim \ln N_{ch}$, the gas is dimerized, i.e. consists of bound neutral pairs. At lower temperatures, $\ln N_{ch} \gtrsim G(L_T) \gtrsim 1$, the pairs overlap and form a Coulomb plasma. The crossover between the two regimes occurs at a parametrically large conductance $G(L_T) \sim \ln N_{ch}$, and may be studied independently from the perturbative effects. Specializing to the high temperature regime, we obtain the leading nonperturbative correction to the wire heat capacity. Its ratio to the heat capacity for noninteracting electrons, C_0, is $\delta C/C_0\sim N_{ch}G^2(L_T)e^{-2G(L_T)}$.Comment: 18 page

Universal and non-universal tails of distribution functions in the directed polymer and KPZ problems

The optimal fluctuation approach is applied to study the most distant (non-universal) tails of the free-energy distribution function P(F) for an elastic string (of a large but finite length L) interacting with a quenched random potential. A further modification of this approach is proposed which takes into account the renormalization effects and allows one to study the most close (universal) parts of the tails. The problem is analyzed for different dimensions of a space in which the polymer is imbedded. In terms the stochastic growth problem, the same distribution function describes the distribution of heights in the regime of a non-stationary growth in a situation when an interface starts to grow from a flat configuration.Comment: 17 pages, 2 figures, the final version, two paragraphs added to the conclusio

Helium Porosity Formation in Vanadium Alloys of V-Ti-Cr, V-W-Zr and V-W-Ta Systems in Comparison with Binary Alloys

Vanadium alloys are considered candidates for use as structural materials of fusion reactors. A large amount of helium will be accumulated in such materials. The presence of helium in the materials may result in gas swelling. This paper presents the results on helium porosity formation researches in V–Ti–Cr, V–W–Zr and V–W–Ta alloys obtained by means of TEM. Samples were irradiated by 40 keV Не+ ions up to dose of 5 ⋅ 1020m−2 at 923 K. Alloy V–4%Ti–4%Cr has a smallest helium swelling among the ternary alloys and its swelling is significantly lower than swelling of dual V–Ti and V–Cr alloys. The swelling of the ternary V–2%W–1%Zr alloy is more than 3 times less than the swelling of vanadium, several times less than that of V–W alloys and slightly lower than the swelling of V– Zr alloys. Swelling increases by a factor of 1.5 with increasing of Zr content to 2% in the ternary V–2%W–1%Zr alloy. Similarly, gas swelling of ternary V–2%W–1%Ta alloy is significantly lower than that for binary V–W and V–Ta alloys. Assumptions are made about the possible mechanisms of the effect of alloying elements in vanadium on helium porosity formation. Keywords: vanadium alloys, swelling, helium, radiation resistance