We report results of a new technique to measure the electric dipole moment of 129 Xe with 3 He comagnetometry. Both species are polarized using spin-exchange optical pumping, transferred to a measurement cell, and transported into a magnetically shielded room, where SQUID magnetometers detect free precession in applied electric and magnetic fields. The result from a one week measurement campaign in 2017 and a 2.5 week campaign in 2018, combined with detailed study of systematic effects, is dA( 129 Xe) = (1.4 ± 6.6stat ± 2.0syst) × 10 −28 e cm. This corresponds to an upper limit of |dA( 129 Xe)| < 1.4 × 10 −27 e cm (95% CL), a factor of five more sensitive than the limit set in 2001.Searches for permanent electric dipole moments (EDMs) are a powerful way to investigate beyondstandard-model (BSM) physics. An EDM is a charge asymmetry along the total angular momentum axis of a particle or system and is odd under both parity reversal (P) and time reversal (T). Assuming CPT conservation (C is charge conjugation), an EDM is a direct signal of CP violation (CPV), a condition required to generate the observed baryon asymmetry of the universe [1]. The Standard Model incorporates CPV through the phase in the CKM matrix and the QCD parameterθ. However, the Standard Model alone is insufficient to explain the size of the baryon asymmetry [2]. BSM scenarios that generate the observed baryon asymmetry [3] generally also provide for EDMs larger than the SM estimate, which for 129 Xe is |d A ( 129 Xe) SM | ≈ 5 × 10 −35 e cm [4].EDM measurements have provided constraints on how BSM CPV can enter low-energy physics [4]. Diamagnetic systems such as 129 Xe and 199 Hg are particularly sensitive to CPV nucleon-nucleon interactions that induce a nuclear Schiff moment and CPV semileptonic couplings [7]. While the most precise atomic EDM measurement is from 199 Hg [8], there are theoretical challenges to constraining hadronic CPV parameters from 199 Hg alone, and improved sensitivity to the 129 Xe EDM would tighten these constraints [7,9]. Additionally, recent work has shown that contributions from light-axion-induced CPV are significantly stronger for 129 Xe than for 199

Inelastic X-ray scattering with meV energy resolution (IXS) is an ideal tool to measure collective excitations in solids and liquids. In non-resonant scattering condition, the cross-section is strongly dominated by lattice vibrations (phonons). However, it is possible to probe additional degrees of freedom such as magnetic fluctuations that are strongly coupled to the phonons. The IXS spectrum of the coupled system contains not only the phonon dispersion but also the so far undetected magnetic correlation function. Here we report the observation of strong magnon–phonon coupling in LiCrO2 that enables the measurement of magnetic correlations throughout the Brillouin zone via IXS. We find electromagnon excitations and electric dipole active two-magnon excitations in the magnetically ordered phase and heavily damped electromagnons in the paramagnetic phase of LiCrO2. We predict that several (frustrated) magnets with dominant direct exchange and non-collinear magnetism show surprisingly large IXS cross-section for magnons and multi-magnon processes.

We determine the phase diagram of copper nitrate Cu(NO3)2·2.5D2O in the context of quantum phase transitions and novel states of matter. We establish this compound as an ideal candidate to study quasi-1D Luttinger liquids, 3D Bose-Einstein-Condensation of triplons, and the crossover between 1D and 3D physics. Magnetocaloric effect, magnetization, and neutron scattering data provide clear evidence for transitions into a Luttinger liquid regime and a 3D long-range ordered phase as function of field and temperature. Theoretical simulations of this model material allow us to fully establish the phase diagram and to discuss it in the context of dimerized spin systems.PACS numbers: 75.10. Jm, 75.30.Sg, 75.40.Cx There has been a flourish of interest in quantum antiferromagnets of late, due to a fascinating range of novel ground states as well as a multitude of exotic fieldinduced phases. A current focus of these studies involves materials with a reduced dimensionality. In particular, one-dimensional (1D) systems [1] have been shown to exhibit remarkable properties such as Luttinger liquid (LL) behavior, a concept relevant to a wide range of systems including quantum wires or nanotubes [2,3]. In this context, magnetic insulators such as the gapless uniform spin chain KCuF 3 [4] have been used as model systems allowing extensive studies of LLs.Presently, of particular interest are spin S = 1 2 alternating antiferromagnetic chain systems. Here, an antiferromagnetic coupling J 1 leads to a formation of spin pairs (dimers) while a weaker antiferromagnetic interdimer exchange J 2 couples the dimers along one dimension. Thus, the system is described in an external field h by the HamiltonianBecause of the dimer formation, such materials exhibit a singlet ground state separated from a low lying triplet of finite width by an energy gap, ∆. The gap is closed by the application of a magnetic field which Zeemansplits the triplet into its three constituents. At the critical field H c1 , the lower S z = 1 mode starts to collapse into the ground state, while at a second critical field H c2 the S z = 1 triplet state has fully shifted below the singlet and a gap reopens. Between the two critical fields a LL of interacting triplets develops.At very low temperatures, and with a weak interchain interaction J ′ present in real materials, the triplet states (triplons) condense into a long-range ordered (LRO) ground state between the two critical fields, a phase that is described as Bose-Einstein-condensation (BEC) of triplons [5][6][7]. The concept of a BEC of triplons was first introduced for the 3D interacting dimer system TlCuCl 3 [8], and later extended to other 2D or 3D coupled dimer systems [9,10]. Quasi-1D materials involving alternating spin chains or ladders, in addition, may show evidence of both LL and BEC phases [11]. Therefore they would allow the unique opportunity to study crossover effects between 1D and 3D physics. Only the ladder series (Hpip) 2 Cu(Br,Cl) 4 is discussed in terms of such a dimensional crossover from a LL ...

In the high spin–orbit-coupled Sr2IrO4, the high sensitivity of the ground state to the details of the local lattice structure shows a large potential for the manipulation of the functional properties by inducing local lattice distortions. We use epitaxial strain to modify the Ir–O bond geometry in Sr2IrO4 and perform momentum-dependent resonant inelastic X-ray scattering (RIXS) at the metal and at the ligand sites to unveil the response of the low-energy elementary excitations. We observe that the pseudospin-wave dispersion for tensile-strained Sr2IrO4 films displays large softening along the [h,0] direction, while along the [h,h] direction it shows hardening. This evolution reveals a renormalization of the magnetic interactions caused by a strain-driven cross-over from anisotropic to isotropic interactions between the magnetic moments. Moreover, we detect dispersive electron–hole pair excitations which shift to lower (higher) energies upon compressive (tensile) strain, manifesting a reduction (increase) in the size of the charge gap. This behavior shows an intimate coupling between charge excitations and lattice distortions in Sr2IrO4, originating from the modified hopping elements between the t2g orbitals. Our work highlights the central role played by the lattice degrees of freedom in determining both the pseudospin and charge excitations of Sr2IrO4 and provides valuable information toward the control of the ground state of complex oxides in the presence of high spin–orbit coupling.