Closing in on a Magnetic Analog of Liquid Crystals

Abstract

We report a 51 V nuclear magnetic resonance investigation of the frustrated spin-1=2 chain compound LiCuVO 4 , performed in pulsed magnetic fields and focused on high-field phases up to 56 T. For the crystal orientations H∥c and H∥b, we find a narrow field region just below the magnetic saturation where the local magnetization remains uniform and homogeneous, while its value is field dependent. This behavior is the first microscopic signature of the spin-nematic state, breaking spin-rotation symmetry without generating any transverse dipolar order, and is consistent with theoretical predictions for the LiCuVO 4 compound. DOI: 10.1103/PhysRevLett.118.247201 The search for new states of quantum matter is one of the most active research fields in condensed-matter physics. In this respect, frustrated magnetic systems attract a lot of interest as they accommodate various unconventional quantum states, having no direct classical analogues, ordered and disordered, induced by the competing interactions [1]. One particularly interesting state is the spinnematic phase, in which the quantum magnet behaves like a liquid crystal. Taking an external magnetic field H as the reference direction, a spin-nematic phase is defined as a state without any transverse dipolar (i.e., vector-type) order,The quadrupolar order parameter develops on the bonds between neighboring spins and can be described as a condensate of two-magnon pairs. It breaks the spinrotational symmetry about the magnetic field, but only partially as π rotations transform the order parameter into itself. The also broken translational symmetry of the order parameter is invisible in the dipolar channel. There is also an analogy between the spin-nematic phase and the superconducting state: the nematic phase can be considered as a "bosonic" superconductor formed as a result of twomagnon condensation [1,2].The concept of a spin-nematic state was developed by Andreev and Grishchuk more than 30 years ago [3], which incited an intense search for a realization in real materials. However, a definite experimental proof for the existence of such a phase has not been provided yet. Several magnetic insulators have been proposed as possible candidates, including the two-dimensional magnet NiGa 2 S 4 (spin-1 system) [4-6] and thin films of 3 He [7][8][9].In the past 10 years a large number of theoretical studies have supported the formation of the spin-nematic phase in frustrated zigzag 1D (chain) systems [10][11][12][13][14]. Among these, orthorhombic LiCuVO 4 is one of the most promising candidates [15,16]. It consists of spin-1=2 Cu 2þ chains along the orthorhombic b axis with a dominant nearestneighbor ferromagnetic interaction J 1 ¼ −1.6 meV, a frustrated next-nearest-neighbor antiferromagnetic interaction J 2 ¼ 3.8 meV, and an interchain coupling J ¼ −0.4 meV [17,18]. At zero magnetic field an incommensurate planar spiral structure is realized below T N ¼ 2.3 K, having the moments lying in the ab plane [19,20]. Above 10 T, an incommensurate, collinear spin-density wave (S...

Possible quadrupolar nematic phase in the frustrated spin chain LiCuSbO4 : An NMR investigation

“…as pointed out in Ref 28. and ESR might reveal excitation of bound magnon pair typical of a QN phase29 .…”

Possible observation of quantum spin-nematic phase in a frustrated magnet

“…There is good theoretical evidence that SN order should occur in a wide range of systems, including thin films of 3 He; cold atoms in an optical lattice; and a wide variety of quantum magnets with competing, or “frustrated,” interactions. The simplest candidate is the spin-1 system in which spin quadrupole moments of spin-1 form a quadrupolar order (2), although its observation is still elusive (3). Among other widely discussed examples are quantum spin chains (4–8) and square-lattice Heisenberg models (9–12) where ferromagnetic first-neighbor interactions ( J 1 ) compete with antiferromagnetic second-neighbor interactions ( J 2 ), in applied magnetic field.…”

Nuclear magnetic resonance in high magnetic field: Application to condensed matter physics

“…The first experiment was done for H c in a steady magnetic field [105], using the hybrid magnet at Tallahassee. It was concluded that the anomalous phase observed by magnetisation was essentially due to impurities, most of the system being saturated above 41.4 T, and that the nematic phase, if present, could only exist between 40.5 T < H < 41.4 T. However, very recent experiments conducted in pulsed magnetic field for H c and H b have shown that, in both orientations, there is a field range below the saturation field in which there is no transverse order and the observed field dependence of the hyperfine shift is identical to the change in the magnetic susceptibility [37,106], in agreement with the theoretical To each site correspond 6 lines due to the two isotopes 63 Cu and 65 Cu and the quadrupole coupling, which does not depend on the site. Note that the width of stability of the plateau is only 1.5 T which precludes any field sweep at constant frequency to obtain the full spectrum.…”