arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2002.08107cond-mat.supr-concond-mat.mes-hall
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薄膜中量子超导-金属转变附近的奇异金属态

Strange metal state near quantum superconductor-metal transition in thin films

Konstantin Tikhonov, Mikhail Feigel'man

摘要:

我们开发了一个理论的量子$T = 0$相变(q-SMT)之间的金属和超导基态在一个二维金属冻结在空间波动$δλ(r)$的库珀吸引常数。当涨落强度$δλ(r)$超过某个临界值时,由于超导相的局部液滴的自发形成,q-SMT的通常的类平均场情形被打破。这些液滴的密度随平均吸引常数$λ$的增加呈指数增长。液滴有序参数之间的相互作用是由于邻近效应通过正常的金属和尺度与距离$\propto 1/r^β$,与$2 < β\le 3$。我们通过实空间强无序重整化群(RG)来解释这种相互作用。在q-SMT附近,RG流在形式上是Kosterlitz无边界RG的对偶等价物。对应的固定点线描述了具有超导岛的大分形簇的金属的格里菲斯相。群集中的岛的典型数量按$N_δ\sim 1/δ$增长,其中$0 < δ\ll 1 $是到临界点的距离。超导侧描述了一个失控的RG轨迹进入强耦合区。靠近SC侧的过渡点$0<-δ\ll 1$,RG轨迹具有作为RG参数$|δ|^{1/2} \ln(1/Tτ)$的函数的极值。它导致在宽的温度范围内的物理性能几乎是$T$独立的。这一观察结果可能与理解q-SMT附近经常观察到的\emph{strange metal}状态有关。

英文摘要:

We develop a theory of quantum $T = 0$ phase transition (q-SMT) between metal and superconducting ground states in a two-dimensional metal with frozen-in spatial fluctuations $δλ(r)$ of the Cooper attraction constant. When strength of fluctuations $δλ(r)$ exceeds some critical magnitude, usual mean-field-like scenario of the q-SMT breaks down due to spontaneous formation of local droplets of superconducting phase. The density of these droplets grows exponentially with the increase of average attraction constant $λ$. Interaction between the droplet's order parameters is due to proximity effect via normal metal and scales with distance $\propto 1/r^β$ , with $2 < β\le 3$. We account for this interaction by means of a real-space strong-disorder renormalization group (RG). Near the q-SMT the RG flow is, formally, a dual equivalent of the Kosterlitz-Thouless RG. The corresponding line of fixed points describes a Griffiths phase of a metal with large fractal clusters of superconducting islands. Typical number of islands in a cluster grows as $N_δ\sim 1/δ$, where $0 < δ\ll 1 $ is the distance to the critical point. Superconducting side is described by a runaway of RG trajectories into the strong-coupling region. Close to the transition point on the SC side, $0<-δ\ll 1$, RG trajectories possess an extremum as function of the RG parameter $|δ|^{1/2} \ln(1/Tτ)$. It results in a wide temperature range where physical properties are nearly $T$-independent. This observation may be relevant to the understanding of a \emph{strange metal} state frequently observed near q-SMT.

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