Search

As to the prototypical realization of the famous Mermin–Wagner theorem, two dimensional Heisenberg ferromagnets (2D HFMs) are expected to have no static order at finite temperatures [N. D. Mermin and H. Wagner, Phys. Rev. Lett., 1966, 17, 1133]. However, a perfect 2D HFM with negligible inter-layer exchange is still lacking, impeding studies of its novel properties. Here we report the synthesis, structure, and properties of a new metal–organic single crystal piperazinediium tetrabromocuprate ((C4H12N2)CuBr4, PTBC). The Cu2+ spins form perfect 2D layers which are well separated by organic ligands. Single crystal electron paramagnetic resonance (EPR) and magnetic susceptibility measurements reveal that PTBC is a highly isotropic Heisenberg ferromagnet with a strong intra-layer ferromagnetic exchange J/kB = 31.34(6) K (H‖ab) and 36.54(17) K (H⊥ab). However, it does not order down to 2 K, indicating the negligible inter-layer exchange J′ and ultra-small R ratio (R = J′/J) below 6 × 10−28. This is the smallest R ratio ever reported for a 2D HFM. These results imply that PTBC is by far the best realization of a 2D HFM system. Moreover, the typical single crystal size is as large as 20 mm × 20 mm × 3 mm, making it suitable for studying the magnetic dynamics of a 2D HFM by probes such as inelastic neutron scattering.

It has been well documented that changes in ion fluxes across cellular membranes is fundamental in maintaining cellular homeostasis. Dysregulation and/or malfunction of ion channels are critical events in the pathogenesis of diverse diseases, including cancers. In this study, we focused on the study of K+ channels in hepatocellular carcinoma (HCC). By data mining TCGA cohort, the expression of 27 K+ channels was investigated and KCNJ11 was identified as a key dysregulated K+ channels in HCC. KCNJ11 was differentially expressed in HCC and predicted a poor prognosis in HCC patients. Inhibition of NFκB signaling suppressed KCNJ11 expression in HCC cells. Knockdown of KCNJ11 expression inhibited cell proliferation, promoted cell apoptosis, and reduced cell invasive capacity. Mechanistically, we found that KCNJ11 promotes tumor progression through interaction with LDHA and enhancing its enzymatic activity. Pharmacological inhibition of LDHA largely compromised the oncogenic function of KCNJ11 in cell proliferation, cell apoptosis, and cell invasion. Collectively, our data, as a proof of principle, demonstrate that KCNJ11 acts as an oncogene in HCC though forming a complex with LDHA and suggest that targeting KCNJ11 can be developed as a candidate tool to dampen HCC.

First-principles calculations are performed to study the hole doping effect in a series of iron arsenic superconductors, such as the undoped CaFe2As2, CaFeAsF, and the hole-doped CaKFe4As4, KCa2Fe4As4F2, and KFe2As2. Charge occupations in the Fe 3d orbitals are found to show opposite variations when the filling is changed. Compared with the undoped CaFe2As2 and CaFeAsF, charges of the and orbitals decrease while those of the and d xy orbitals increase in the hole-doped materials CaKFe4As4, KCa2Fe4As4F2 and KFe2As2. By further analyzing the Pauli susceptibilities of CaFe2As2 and CaFeAsF, instability is found at the wave vector of , which is responsible for the stripe type antiferromagnetic order. In contrast, the Pauli susceptibilities of CaKFe4As4 and KCa2Fe4As4F2 at are strongly suppressed while the instabilities remain around , which may be the origin of superconductivity. Combining with the calculated orbital-resolved Pauli susceptibility, we conclude that hole doping mainly results in a decrease of charge occupations in the and orbitals, and these three orbitals play dominant roles in controlling the magnetic and superconducting properties in these iron-based superconductors.

In iron-based superconductors, unravelling the origin of the antiferromagnetism is a crucial step towards understanding the high-Tc superconductivity as it is widely believed that the magnetic fluctuations play important roles in the formation of the Cooper pairs. Therefore, in this paper, we will briefly review experimental results related to the antiferromagnetic state in iron-based superconductors and focus on a review of the theoretical investigations which show applicability of the itinerant scenario to the observed antiferromagnetism and corresponding phase transitions in various families of the iron-based superconductors. A proposal of coupling between frustrated and unfrustrated bands for understanding the reduced magnetic moment typically observed in iron pnictides is also reviewed. While all the above theoretical investigations do not rule out a possible existence of localized electrons in iron-based superconductors, these results strongly indicate a close relation between itinerant electrons and the magnetically ordered state and point out the importance of taking into account the orbital degrees of freedom.

By applying density functional theory calculations to iron chalcogenides, we find that magnetic order in Fe$_{1+y}$Te and magnetic instability at $(\pi,\pi)$ in K$_y$Fe$_2$Se$_2$ are controlled by interstitial and interlayer cations, respectively. While in Fe$_{1+y}$Te, magnetic phase transitions occur among collinear, exotic bicollinear and plaquette-ordered antiferronmagnetic states when the height of interstitial irons measured from iron plane or the concentration of interstitial irons is varied, the magnetic instability at $(\pi,\pi)$ which is believed to be responsible for the Cooper pairing in iron pnictides is significantly enhanced when $y$ is much smaller than $1$ in K$_y$Fe$_2$Se$_2$. Our results indicate that, similar to iron pnictides, itinerant electrons play important roles in iron chalcogenides, even though the fluctuating local moments become larger., Comment: 8 pages, 5 figures

The analytic response theory at density functional theory level is applied to investigate one-photon and two-photon absorption properties of a series of recently synthesized pyrene-core derivatives. The theoretical results show that there are a few charge-transfer states for each compound in the lower energy region. The one-photon absorption properties of the five investigated compounds are highly consistent with those given by experimental measurements. The two-photon absorption intensities of the compounds are greatly enhanced with the increments of the molecular sizes, in which the two-photon absorption cross section of the four-branched compound is about 5.6 times of that of the mono-branched molecule. Furthermore, it is shown that the two-photon absorption properties are sensitive to the geometrical arrangements.

In iron-based superconductors, unravelling the origin of the antiferromagnetism is a crucial step towards understanding the high-Tc superconductivity as it is widely believed that the magnetic fluctuations play important roles in the formation of the Cooper pairs. Therefore, in this paper, we will briefly review experimental results related to the antiferromagnetic state in iron-based superconductors and focus on a review of the theoretical investigations which show applicability of the itinerant scenario to the observed antiferromagnetism and corresponding phase transitions in various families of the iron-based superconductors. A proposal of coupling between frustrated and unfrustrated bands for understanding the reduced magnetic moment typically observed in iron pnictides is also reviewed. While all the above theoretical investigations do not rule out a possible existence of localized electrons in iron-based superconductors, these results strongly indicate a close relation between itinerant electrons and the magnetically ordered state and point out the importance of taking into account the orbital degrees of freedom.

We propose that the contrasting low-temperature behaviors observed experimentally among isostructural and isoelectronic materials, like nonsuperconducting and nonmagnetic MgFeGe, magnetically ordered NaFeAs, and superconducting LiFeAs, can be well understood from itinerant weak-coupling limit. We find that stronger $(\ensuremath{\pi},\ensuremath{\pi})$ instability appearing in the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital of NaFeAs is responsible for the occurrence of weak magnetism, while weaker but still prominent $(\ensuremath{\pi},\ensuremath{\pi})$ instability in LiFeAs leads to a superconducting state. In contrast, multiple competing instabilities coexisting in orbital-resolved momentum-dependent susceptibilities, serving as magnetic frustrations from itinerant electrons, may account for the nonmagnetic state in MgFeGe, while poorer Fermi surface nesting leads to a nonsuperconducting state. Based on above findings, we predict a possible way to make MgFeGe a new Fe-based superconductor.

By calculating orbitally resolved Pauli susceptibilities within maximally localized Wannier orbital basis transformed from first principles band structures, we find that magnetism in Fe$_{1+x}$Te still has its itinerant origin even without Fermi surface nesting, provided orbital modulation of particle-hole excitations are considered. This leads to strong magnetic instabilities at wave vector (0,$\pi$)/($\pi$,0) in d$_{xz}$/d$_{yz}$ orbitals that are responsible for the bicollinear antiferromagnetic state as extra electrons donated from excess Fe are considered. Magnetic exchange coupling between excess Fe and in-plane Fe further stabilizes the bicollinear antiferromagnetic order. Our results reveal that magnetism and superconductivity in iron chalcogenides may have different orbital origin, as Pauli susceptibilities of different orbitals evolve differently as a function of concentration of excess Fe and height of the chalcogen atom measured from the iron plane.