Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro, RJ, Brazil.
J Phys Condens Matter. 2010 Dec 8;22(48):485701. doi: 10.1088/0953-8984/22/48/485701. Epub 2010 Nov 16.
In fermionic systems with different types of quasi-particles, attractive interactions can give rise to exotic superconducting states, such as pair density wave (PDW) superconductivity and breached pairing. In recent years the search for these new types of ground states in cold atoms and in metallic systems has been intense. In the case of metals the different quasi-particles may be the up and down spin bands in an external magnetic field or bands arising from distinct atomic orbitals that coexist at a common Fermi surface. These systems present a complex phase diagram as a function of the difference between the Fermi wavevectors of the different bands. This can be controlled by external means, varying the density in the two-component cold atom system or, in a metal, by applying an external magnetic field or pressure. Here we study the zero temperature instability of the normal system as the Fermi wavevector mismatch of the quasi-particles (bands) is reduced and find a second order quantum phase transition to a PDW superconducting state. From the nature of the quantum critical fluctuations close to the superconducting quantum critical point (SQCP), we obtain its dynamic critical exponent. It turns out to be z = 2 and this allows us to fully characterize the SQCP for dimensions d ≥ 2.
在具有不同类型准粒子的费米子系统中，吸引力相互作用可以导致奇异超导状态，例如对密度波 (PDW) 超导和配对破坏。近年来，人们一直在强烈地寻找冷原子和金属系统中的这些新型基态。在金属中，不同的准粒子可能是外磁场中的上下自旋能带，或者是共存于共同费米面的来自不同原子轨道的能带。这些系统呈现出复杂的相图，作为不同能带费米波矢差的函数。这可以通过外部手段来控制，通过改变两分量冷原子系统的密度，或者在金属中通过施加外磁场或压力来实现。在这里，我们研究了准粒子（能带）的费米波矢失配减小时正常系统的零温不稳定性，并发现了到 PDW 超导态的二级量子相变。从接近超导量子临界点 (SQCP) 的量子临界涨落的性质，我们得到了它的动态临界指数。结果是 z = 2，这使得我们能够完全描述维度 d ≥ 2 的 SQCP。
