In-plane electronic anisotropy of underdoped ‘122’ Fe-arsenide superconductors revealed by measurements of detwinned single crystals

Abstract

The parent phases of the Fe-arsenide superconductors harbor an antiferromagnetic ground state. Significantly, the Néel transition is either preceded or accompanied by a structural transition that breaks the four fold symmetry of the high-temperature lattice. Borrowing language from the field of soft condensed matter physics, this broken discrete rotational symmetry is widely referred to as an Ising nematic phase transition. Understanding the origin of this effect is a key component of a complete theoretical description of the occurrence of superconductivity in this family of compounds, motivating both theoretical and experimental investigation of the nematic transition and the associated in-plane anisotropy. Here we review recent experimental progress in determining the intrinsic in-plane electronic anisotropy as revealed by resistivity, reflectivity and ARPES measurements of detwinned single crystals of underdoped Fe arsenide superconductors in the "122" family of compounds.

Order parameter fluctuation and ordering competition in Ba1−xKxFe2As2

“…Extensive experiments have confirmed that nematic order exists in almost all FeSCs [2][3][4][5][13][14][15][16][17]. In most cases, the nematic order sets in at a temperature T n slightly higher than the critical temperature of magnetic order T m [4,6,10,18,19]. Usually, the magnetic order is generated by a stripe-type SDW, and possesses two characteristic vectors Q X = (π, 0) and Q Y = (0, π) in the Brillouin zone of the iron square lattice, which relate to the spin operator S(r) in the form S(r) = M X,Y e iQX,Y ·r [12,20].…”

“…This stripe SDW breaks the discrete lattice rotational symmetry by selecting out only one of the two characteristic vectors Q X and Q Y , preserving the C 2 symmetry [6,8,10,12]. Because the nematic order and SDW order coexist over a large part of the global phase diagram, it is widely believed [3][4][5][6][8][9][10][11][12] that the nematic order is actually induced by the fluctuation of magnetic order.…”

“…A universal property shared by most known iron-based superconductors (FeSCs) is the bulk coexistence of two or even more distinct long-range orders [1][2][3][4][5][6][7][8][9][10][11][12], such as superconductivity, stripe-type spin-density-wave (SDW) order, nematic order, and other possible orders. The competition and coexistence of these orders leads to a very complicated global phase diagram [1][2][3][4][5][6][7][8][9][10][11][12].…”

“…The competition and coexistence of these orders leads to a very complicated global phase diagram [1][2][3][4][5][6][7][8][9][10][11][12]. Acquiring a detailed knowledge of the phase diagram is an important step towards a better understanding of FeSCs.…”

Direct observation of the depairing current density in single-crystalline Ba0.5K0.5Fe2As2 microbridge with nanoscale thickness

“…Note that for T ≤37 K, when the current returns along a resistive branch back to the SC state at a return current I r , a pronounced hysteresis of IVCs demonstrates a Josephson-junction-like behavior [9]. However, the single crystal was confirmed to be of high quality in previous work [14], and we selected the optimally-doped Ba 0.5 K 0.5 Fe 2 As 2 which should not have a nematic state as the under-doped state [19], thus grains or twin boundaries can be also ruled out. In addition, the micro-device has well-designed geometry as shown in the inset of Fig.…”