Bounded Luttinger liquids as a universality class of quantum critical behavior

We show that one-dimensional quantum systems with gapless degrees of freedo m and open boundary conditions form a universality class of quantum critica l behavior, which we propose to call ''bounded Luttinger liquids." They sha re the following properties with ordinary (periodic) Luttinger liquids: the absence of fermionic quasiparticle excitations, charge-spin separation, an d anomalous power-law correlations with exponents whose scaling relations a re parametrized by a single coupling constant per degree of freedom, K-nu. The values of K-nu are independent of boundary conditions, but the represen tation of the critical exponents in terms of these K-nu's depends on bounda ry conditions. We illustrate these scaling relations by exploring general r ules for boundary critical exponents derived earlier using the Bethe ansatz solution of the one-dimensional Hubbard model together with boundary confo rmal held theory, and the theory of Luttinger liquids in finite-size system s. We apply this theory to the photoemission properties of the organic cond uctors (TMTSF)(2)X, where TMTSF is tetramethyltetraselenafulvalene, and X = ClO9, PF6, ReO4, and discuss to what extent the assumption of finite stran ds with open boundaries at the sample surface can reconcile the experimenta l results with independent information on the Luttinger-liquid state in the se materials.