(13)C nuclear magnetic resonance measurements were performed on κ-(BEDT-TTF)(2)Cu(NCS)(2), with the external field placed parallel to the quasi-2D conducting layers. The absorption spectrum is used to determine the electronic spin polarization M(s) as a function of external field H at a temperature T=0.35 K. A discontinuity in the derivative dM(s)/dH at an applied field of H(s)=213±3 kOe is taken as evidence for a Zeeman-driven transition within the superconducting state and stabilization of inhomogeneous superconductivity.
We report a 51 V nuclear magnetic resonance investigation of the frustrated spin-1/2 chain compound LiCuVO4, performed in pulsed magnetic fields and focused on high-field phases up to 55 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 LiCuVO4 compound.PACS numbers: 75.10. Kt, 75.30.Kz, 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 spin-nematic 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, (−1) i S + i + H.c. = 0, but possessing instead a transverse quadrupolar (tensor-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 spin-rotational 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 two-magnon condensation [1,2].The concept of a spin-nematic state was developed by Andreev and Grishchuk more than 30 years ago [3], which incited 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 spinnematic phase in frustrated zig-zag 1D (chain) systems [10][11][12][13][14]. Amongst these, orthorhombic LiCuVO 4 is one of the most promising candidates [15,16]. It consists of spin-1/2 Cu 2+ chains along the orthorhombic b axis with a dominant nearest-neighbor ferromagnetic interaction J 1 = −1.6 meV, a frustrated next-nearest-neighbor antiferromagnetic interaction J 2 = 3.8 meV, and an interchain coupling J = −0.4 meV [17,18]. At zero magnetic field an incommensurate planar spiral structure is realized below T N = 2.3 K, having the moments lying...
From the measurement and analysis of the specific heat of high-quality K1−xNaxFe2As2 single crystals we establish the presence of large T 2 contributions with coefficients αsc ≈ 30 mJ/mol K In spite of the substantial experimental and theoretical research efforts to elucidate the symmetry and magnitude of the superconducting order parameter for the Fe pnictides [1, 2], important questions concerning the doping evolution of the superconducting gap remain unsolved [3,4]. In the stoichiometric parent compounds nesting usually occurs between electron (el) and hole (h) Fermi surface sheets (FSS) which is responsible for the presence of long-range spin density wave (SDW) order. Superconductivity (SC) emerges when the SDW order is suppressed by doping or external pressure [2]. An s ± gap symmetry (nodeless gap function with opposite signs of the order parameters for el and h pockets) is believed to be realized in under-and optimally doped compounds, since the antiferromagnetic spin fluctuations (SF) on the vector Q = (π, π) connecting the el and h pockets remain strong in the vicinity of the SDW phase. The situation in the overdoped regime is not so clear. With further doping, el (h) bands disappear. Therefore, the paradigm of the SF glue at the vector Q = (π, π) does not work. However, SF have been found at some incommensurate propagation vectors [5]. This has led to several proposals for the order parameters in heavily doped compounds: extended s, d, s + id wave [3,[6][7][8]. Thus, even from theoretical perspective the situation is still controversial.One of the most interesting families from this point of * M.A. and V.G. have equally contributed to the present paper.
Commissioning studies of the CMS hadron calorimeter have identified sporadic uncharacteristic noise and a small number of malfunctioning calorimeter channels. Algorithms have been developed to identify and address these problems in the data. The methods have been tested on cosmic ray muon data, calorimeter noise data, and single beam data collected with CMS in 2008. The noise rejection algorithms can be applied to LHC collision data at the trigger level or in the offline analysis. The application of the algorithms at the trigger level is shown to remove 90% of noise events with fake missing transverse energy above 100 GeV, which is sufficient for the CMS physics trigger operation.
In the heavy-fermion metal CePdAl long-range antiferromagnetic order coexists with geometric frustration of one third of the Ce moments. At low temperatures the Kondo effect tends to screen the frustrated moments. We use magnetic fields B to suppress the Kondo screening and study the magnetic phase diagram and the evolution of the entropy with B employing thermodynamic probes. We estimate the frustration by introducing a definition of the frustration parameter based on the enhanced entropy, a fundamental feature of frustrated systems. In the field range where the Kondo screening is suppressed the liberated moments tend to maximize the magnetic entropy and strongly enhance the frustration. Based on our experiments, this field range may be a promising candidate to search for a quantum spin liquid.If competing exchange interactions prevent magnetic systems from developing long-range order, the frustrated magnetic moments can form fluid-like states of matter, so-called spin liquids (SLs) [1]. If the moments act as effective spin-1/2 particles, quantum fluctuations dominate and impede the moments from freezing or ordering at low temperatures T [2]. The ground states of these quantum SLs are characterized by massive many-body entanglement rendering them particularly attractive for investigations of new types of quantum matter. Ever since the first notion of SLs was advertised, there has been continual effort to search for materials that might host SLs, mainly in geometrically frustrated magnets [3][4][5][6][7]. Up to now only very few candidates for metallic SLs have been discovered [2, 8].CePdAl belongs to a class of heavy-fermion (HF) metals with ZrNiAl-type crystal structure (space group P62m) that display geometric frustration owing to the fact that the Ce ions form a distorted kagomé network in the hexagonal ab plane [9][10][11]. In HF compounds the magnetic moments are formed by nearly localized 4f or 5f states. Magnetic correlations are enabled by the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction which competes with the Kondo effect tending to screen the moments at low T . The presence of a Kondo effect in CePdAl is manifest through a logarithmic increase of the resistivity with decreasing T [12, 13] and an extremum of the thermopower at low T [14-16].CePdAl stands out due to the coexistence of geometric frustration with antiferromagnetic (AF) order below T N = 2.7 K [9, 14]. Neutron diffraction experiments [9] and 27 Al NMR measurements [17] reveal that one third of the Ce moments do not participate in the longrange order down to 30 mK. Theoretical models considering a quasi-two-dimensional magnetic structure based on the neutron experiments performed on polycrystals [9] suggest that the Ce moments of the hexagonal basal plane order in ferromagnetic chains which are antiferromagnetically coupled and separated from each other by the frustrated, interjacent moments [inset of Fig. 1(b)] [18, 19]. In the c direction this structure is repeated with an incommensurate AF modulation. Due to the crystal-electric...
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