Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Phonon-induced rotation of the electronic nematic director in
  superconducting Bi$_{2}$Se$_{3}$   The doped topological insulator $A_{x}\mathrm{Bi_{2}Se_{3}}$, with
$A=\{\mathrm{Cu},\mathrm{Sr},\mathrm{Nb}\}$, becomes a nematic superconductor
below $T_{c}\sim3-4\,\mathrm{K}$. The associated electronic nematic director is
described by an angle $\alpha$ and is experimentally manifested in the
elliptical shape of the in-plane critical magnetic field $H_{c2}$. Because of
the threefold rotational symmetry of the lattice, $\alpha$ is expected to align
with one of three high-symmetry directions corresponding to the in-plane
nearest-neighbor bonds, consistent with a $Z_{3}$-Potts nematic transition.
Here, we show that the nematic coupling to the acoustic phonons, which makes
the nematic correlation length tend to diverge along certain directions only,
can fundamentally alter this phenomenology in trigonal lattices. Compared to
hexagonal lattices, the former possesses a sixth independent elastic constant
$c_{14}$ due to the fact that the in-plane shear strain doublet
$(\epsilon_{xx}-\epsilon_{yy},-2\epsilon_{xy})$ and the out-of-plane shear
strain doublet $(2\epsilon_{yz},-2\epsilon_{xz})$ transform as the same
irreducible representation. We find that, when $c_{14}$ overcomes a threshold
value, which is expected to be the case in doped $\mathrm{Bi_{2}Se_{3}}$, the
nematic director $\alpha$ unlocks from the high-symmetry directions due to the
competition between the quadratic phonon-mediated interaction and the cubic
nematic anharmonicity. This implies the breaking of the residual in-plane
twofold rotational symmetry ($C_{2x}$), resulting in a triclinic phase. We
discuss the implications of these findings to the structure of nematic domains
and to the shape of the in-plane $H_{c2}$ in $A_{x}\mathrm{Bi_{2}Se_{3}}$, and
to presence of nodes inside the superconducting state.

1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
22
The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
13
The categories of this paper are: quant-ph
16
The categories of this paper are: stat
12
The categories of this paper are: nucl-th
26
The categories of this paper are: bayes-an
2
The categories of this paper are: math
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
24
The categories of this paper are: dg-ga