Raman phonon anomalies in Sr(Fe_(1-x)Co_(x))_(2)As_(2)

Phonon anomalies have been reported in iron-pnictide superconductors indicating a diverse interplay between different orders in the materials.Here,we report Raman scattering measurements on Sr(Fe_(1-x)Co_(x))_(2)As_(2)(x=0 and x=0.04)single crystals in the B;symmetry with respect to a 1 Fe unit cell.Upon cooling,we observe a larger split(13 cm;)of Eg Raman phonon modes pertaining to in-plane Fe and As displacements as the crystals undergo the tetragonal-toorthorhombic structural phase transition,although a considerable split(9 cm;)has been reported in BaFe_(1-x)Co_(x))_(2)As_(2).Furthermore,the splitting of E;phonon modes is strongly reduced upon doping.We perform an order-parameter analysis revealing a similar doping dependence of E;phonon splitting as reported in other compounds of the 122 family,indicating these phonon anomalies widely exist in 122 iron-based superconductors and might share the same mechanisms.

Muon Spin Relaxation Study of Frustrated Tm_(3)Sb_(3)Mg_(2)O_(14)with Kagomé Lattice

The structure and magnetic properties of rare-earth ions Tm^(3+)Kagomé lattice Tm_(3)Sb_(3)Mg_(2)O_(14)are studied by x-ray diffraction,magnetic susceptibility and muon spin relaxation(𝜇SR)experiments.The existence of a small amount of Tm/Mg site-mixing disorder is revealed.DC magnetic susceptibility measurement shows that Tm^(3+)magnetic moments are antiferromagnetically correlated with a negative Curie-Weiss temperature of−26.3 K.Neither long-range magnetic order nor spin-glass transition is observed by DC and AC magnetic susceptibility,and confirmed by μSR experiment down to 0.1 K.However,the emergence of short-range magnetic order is indicated by the zero-field μSR experiments,and the absence of spin dynamics at low temperatures is evidenced by the longitudinal-field μSR technique.Compared with the results of Tm_(3)Sb_(3)Zn_(2)O_(14),another Tm-based Kagomé lattice with much more site-mixing disorder,the gapless spin liquid like behaviors in Tm_(3)Sb_(3)Zn_(2)O_(14)can be induced by disorder effect.Samples with perfect geometrical frustration are in urgent demand to establish whether QSL exists in this kind of materials with rare-earth Kagomé lattice.

Fluctuating magnetic droplets immersed in a sea of quantum spin liquid

The search of quantum spin liquid(QSL),an exotic magnetic state with strongly fluctuating and highly entangled spins down to zero temperature,is a main theme in current condensed matter physics.However,there is no smoking gun evidence for deconfined spinons in any QSL candidate so far.The disorders and competing exchange interactions may prevent the formation of an ideal QSL state on frustrated spin lattices.Here we report comprehensive and systematic measurements of the magnetic susceptibility,ultralow-temperature specific heat,muon spin relaxation(μSR),nuclear magnetic resonance(NMR),and thermal conductivity for NaYbSe2 single crystals,in which Yb3+ions with effective spin-1/2 form a perfect triangular lattice.All these complementary techniques find no evidence of long-range magnetic order down to their respective base temperatures.Instead,specific heat,μSR,and NMR measurements suggest the coexistence of quasi-static and dynamic spins in NaYbSe2.The scattering from these quasi-static spins may cause the absence of magnetic thermal conductivity.Thus,we propose a scenario of fluctuating ferrimagnetic droplets immersed in a sea of QSL.This may be quite common on the way pursuing an ideal QSL,and provides a brand new platform to study how a QSL state survives impurities and coexists with other magnetically ordered states.